It's been a regular weapon at this year's Championships, no surprise as it is one of the most established systems within queen's pawn games.
Sevian goes for an aggressive system
An early committal decision here from Sam, who weakens his king a bit and delays his development, in order to focus on building the strongest center that he can.
Niemann fights for control of the center immediately, rushing to make it difficult for Sevian to push his king's pawn forward two squares as he intended.
Sevian targets the bishop, happy to invite a piece trade. It's true that his structure would take a hit (with his pawns getting doubled) but the upshot would be that he would gain the bishop pair and a strong central pawn mass.
Niemann takes the game in a different direction, dropping back in order to avoid conceding the bishop pair. It does however cost him quite a bit of time, as he first stepped his bishop out only to now drop it back.
The most consistent
Sevian stays true to the logic of his previous moves, and he pushes his pawn. Without the bishop pinning the knight, he was in a position to do so immediately.
Sevian's king has been left a bit weakened and his position a little loose after this exchange, so he'll have to watch out for tactics. But long-term, he's in great shape here with a big pawn mass in the center that could prove suffocating for Niemann down the line.
Niemann immediately seeks to undermine the center, understanding that he cannot just ignore it as then it would grow into a monster sooner or later.
Sevian secures a passed pawn
He pushes forward, the typical reaction as now he's able to net himself a protected passed pawn.
Niemann trades off a pair of pawns, in part with the idea to open up the diagonal for his light-squared bishop.
A Benoni-like position
In reality, even though the game started off as a Nimzo-Indian, it has morphed into a kind of Benoni Defense. The structure is similar to what you get in that opening, with the White side having more space, but sometimes risking being a bit overextended and having some weak squares in key positions.
Niemann x-rays the king
He indirectly eyes up Sevian's king, hoping to make use of his lead in development.
Sevian covers and develops
This move makes a lot of sense, with Sam looking to mix speedy development with covering against a possible discovered check if Niemann were to move his bishop next.
Niemann steps his bishop out to a strong active square, pinning the knight.
Sevian has that knight solidly defended, so he doesn't need to do anything about the pressure. Instead, he brings his king to safety.
Niemann completes his minor piece development
He emerges from the early opening with healthy piece placement, though for him the long-term concern is whether or not he'll manage to contain that dangerous protected passed pawn that Sevian has established in the center.
Sevian looks to break the pin
Or, at the very least, to force the bishop to go back one square while slightly improving his pawn chain.
Niemann trades off his active bishop for what was a pretty passive knight. Even though that may seem counter-intuitive, it's the right decision. The reason is because otherwise Sevian had the follow-up of bringing his bishop out and controlling the key dark-squared diagonal. So Niemann buys himself time to cut out that plan.
An important move, not only blockading the further advance of the pawn, but ensuring that Sevian cannot dominate that diagonal himself. Niemann may have less central space, but he maintains very solid piece placement. The position is not far from equal.
Sevian develops his final minor piece, challenging Niemann's strong bishop. But piece trades are likely going to be welcomed by Niemann, as the side with less space tends to benefit from them.
Attack and defense
Niemann jumps his queen out, defending his attacked bishop and at the same time targeting Sevian's queenside pawn.
Sevian defends the pawn
He also activates his queen, and connects his rooks. A helpful move, as the pace of the game slows down a little with both players having now largely completed their development.
A typical idea, covering the square that Sevian's knight could potentially jump to. This frees up Niemann to drop his queen back at some point if needed.
Sevian slightly improves his position, setting up a bishop-queen battery to pressure Niemann's kingside.
The fight for the open file
Niemann lifts his rook up, making space for his corner rook (his only undeveloped piece) to come into the game. There's only one open file in the position, so it makes sense to fight to control it.
Sevian flirting with an exchange sacrifice?
One possibility that he's set up is to potentially sacrifice the exchange, which would allow him to damage the defenses of Niemann's king. It seems risky though, as it's a significant amount of material. So if Hans were to weather the storm, then it could lead to ruin long term for Sam. Perhaps it's a case of "the threat being stronger than the execution", at least for now.
Sevian drops back
He's got no interest in taking the knight for now, instead keeping the tension and forcing Niemann to remain with his other knight guarding against the pressure.
Things about to get sharp?!
For now it seems like both players have been playing pretty calmly, just improving their pieces methodically. But now Sevian is lacking plans, other than to harass Niemann's central knight in order to add to the pressure against its pinned colleague. If Sevian does this, Niemann will likely have no choice but to push his pawn to break the pin. And this will lead to a far more messy and chaotic state of affairs!
Too timid
Sevian is getting outplayed in this tricky middlegame. He's now trying to trade off material, a sign that he's bothered by the fact that Hans has the more active pieces.
Niemann bumps up the pressure
I think he senses that Sevian is uncomfortable, and that he has strong chances to fight for the initiative. So he avoids any rook trades, keeping maximum tension on the board.
Under pressure, Sevian makes a significant mistake. His move seems to make a lot of sense, escaping a possible check from Niemann's bishop by placing itself on a light square. However, it has a significant drawback...
This is the problem! Sevian's king, now in the corner, is much more vulnerable to a queen-bishop battery being set up by Hans. And that's exactly what he's going for with his most recent move!
Sevian prepares to meet the battery
He's anticipating that Niemann will bring his queen to the center to threaten checkmate, and so he wants to be able to lift his pawn to block the threat without leaving his bishop stuck on the edge of the board.
A really strong move from Niemann, who recognizes what Sevian is planning and brings his knight to take away that possibility. The threat now of bringing the queen to the center gains tremendously in strength, as Sevian struggles to keep his dark squares together.
Sevian is doing all the right things, cutting out the threatened queen-bishop battery by driving his knight to the central square.
Niemann looks to kick the knight away
He wants to remove the piece, so that he can finally set up the queen-bishop battery he's been looking to build for the past few moves.
A nice touch, as Sevian recognizes that he can afford to give up his knight. The point is that, if Niemann captures it, then he'll be in time to win back the piece by grabbing Niemann's own hanging knight.
Niemann takes care of the threat against his knight, and pressures Sevian's bishop.
Sevian drops back, covering his knight and also his bishop.
A slightly surprising decision, as Niemann's knight was looking quite strong on this advanced square, while Sevian's bishop was clunky due to all of his central pawns being on light squares.
It seems that this is why Niemann was quick to capture the bishop. He wanted to set up the threat of checkmate as soon as possible.
It was important for Sevian not to move the bishop forward, hitting the queen. Had he done that, he would have run into a nasty tactic involving rook takes knight!
The point is that after bishop takes queen, there would have been rook takes queen for Hans! And if instead queen takes rook, then queen takes bishop would have been possible, as the point of the tactic was to eliminate the defender of the bishop (the knight).
Niemann's pawn was under fire, so he brings his pawn forward in order to protect it.
Sevian heading towards the outpost
Sam has definitely made good progress here in recent moves, with his knight now looking to establish itself on the strong central square in the next move or two.
Niemann takes his chance to bring his rook forward onto his own central outpost, before Sevian shuts the door on this plan by jumping his knight forward.
A tense fight
The character of the struggle has definitely shifted in recent moves. With Sevian managing to bring his knight to a strong square, it's no longer the case that he's the one under pressure from Niemann. Instead, both sides have their trumps, with Niemann having pressure against the king but Sevian having the stronger piece placement.
A nice move, centralizing the queen and threatening to bring the rook on to the seventh rank (Sevian's second rank) at the right moment.
Sevian anticipates the threat, and creates one of his own. But it's not clear what he's going to do if Niemann simply moves his pawn up one square to cover against the capture.
In practical terms, Sevian seems to have the much more challenging dynamic to navigate. He's down to just 3 minutes or so on the clock, and won't get extra time (besides the 30 second increment) until move 40!
Niemann covers against the threat.
Sevian looks to make a pawn break
He's trying to drum up some counterplay on the queenside, though I'm not sure what he plans to do if Niemann brings his rook down now and targets his pawn!
Niemann goes a different route, preferring to keep more tension on the board. One idea he might have in mind is to meet the pawn push with a pawn push of his own. Let's take a look...
This is the idea of delivering a pawn push back! If Sevian were to then capture, Niemann could slide his rook over and quickly win back his pawn.
Instead, Niemann decides to capture the pawn. This seems like the least risky option, but then again it allows Sevian to bring his queen to a very active position.
Sevian enters with the queen, creating multiple threats.
Likely what appealed to Niemann about this way of playing, was the possibility to finally exchange Sevian's best piece.
Sevian must be precise
Hans definitely continues to have the initiative here, because of his better (centralized) pieces. But with precise play, Sevian should be able to hold the balance. It's important that he target Niemann's vulnerable pawn next.
In time trouble, Sevian goes wrong. Now, it's easier for Niemann to begin to improve his coordination. And once his king is safe, his centralized queen and rook will cause a lot of problems for Sevian's own monarch.
He needs to recognize that Sevian's plan has not been best here, and that he can play for the win by driving his king up the board. The point is that the checks will then run out, which will free up his pieces to begin causing huge problems to Sevian's position.
Niemann still keeps an edge
He doesn't find the best move, which would have been to bring up his king. The difference is that now, Niemann's bishop is tied down due to the pin against it from Sevian's queen. But still, the position remains very hard to play for Sevian...
They say mistakes come in pairs, and here Sevian plays another inaccuracy as he finds himself under pressure both on the board and on the clock. Now, Hans can snap up his undefended pawn on the queenside!
Just when Niemann seemed to be on the cusp of a big win, he goes horribly wrong and allows Sevian a tactical shot!
This is the problem. Niemann was banking on Sevian not being able to take his rook, since then there would have been checkmate. But now his bishop is hit, and he can't drop it back along the diagonal because of the rook coming down for Sevian with a fatal check!
Niemann must give up his rook
This is what unravels Niemann's position. The bishop had to drop back to this square to safeguard his king. But now Sevian can win the rook, since there's no checkmate because the queen-bishop battery has been broken!
And to make matters worse for Hans, the players have reached move 40. Which means that Sevian gets an extra half an hour to mull over his decision. This looks to be a nasty turnaround, and Hans might well end up suffering his third defeat of the tournament.
Sevian doesn't take too long to think about his move, picking up the rook. Now the position is almost entirely risk-free for Sevian, while he has good chances of eventually overpowering Niemann's defenses.
Niemann takes back, and is now going to have to make the mental shift towards a long and tedious defense, if he's going to have any chance of escaping with a draw.
Niemann is trying his best to harass Sevian's rook before he can coordinate. Hans wants to be able to at least win the pawn that the rook is currently defending, in order to make it hard for Sevian to make a dangerous passed pawn down the line.
Sevian moves the rook away from the attack.
Niemann insists on trying to pick up the pawn on the left-hand side. If Sevian defends it, the problem is that Hans would then have the time to set up the queen-bishop battery once again!
Sevian recognizes that he has no good way of saving the pawn, so he grabs one in exchange. The point is that if Niemann now sets up the queen-bishop battery, Sevian would be in time to force a queen trade!
A nice move
It's a long road for Sevian to break down Niemann's defenses, provided that Hans doesn't blunder. He may be down an exchange, but he does have an extra pawn for his troubles. Niemann's biggest concern is his somewhat shaky king, due to having moved all of his pawns forward one or two squares.
Niemann will have to avoid the queen trade at all costs here, as the endgame of just rook vs bishop (with Sevian having a passed pawn) would be hopeless.
It's a super uncomfortable position for Niemann, who has to constantly watch out for a possible rook slide to whip up an attack along the seventh rank.
Hans in huge trouble
It's understandable that he didn't want to swap queens, as it's hard to believe that he would be able to defend that endgame once Sevian's king came in. But the computer was showing it wouldn't have been easy for Sam to break through, whereas now his attack should be unstoppable.
Every one of Sevian's moves is coming with a nasty threat.
The sad thing for Niemann is that now he is forced to accept the queen trade, but in far worse circumstances than before. This one is going Sam's way.
Looking hopeless
The problem is that Niemann has no way of chasing this pawn down. So Sevian will simply bring his king over, later push his pawn, and eventually break through.
Sevian isn't concerned about Niemann's pawn pushing on the kingside, as he begins to march his king into the game.
Sevian times the pawn push well, since now if he can win the pawn, he'll also be able to grab the base of Niemann's pawn chain on the kingside.
Niemann drops back while keeping Sevian's pawn in his sights. But the problem is that now Sam can end the game on the spot by continuing to push. The pawn will cost Niemann his bishop!
Sam Sevian looked to be in trouble throughout large parts of the game, and it seemed like Hans would be going into the final round on a +2 score.
Two more victories than losses in the tournament wouldn't have left him in bad shape to fight for a podium spot, and he likely would have ended the tournament gaining some rating points as he continues his bid to break into the top 10 in the world.
However, Sam Sevian had other plans! Under pressure, he defended tremendously well and quashed Niemann's many threats while under pressure. He did give Hans a chance or two to cash in on his advantage, but nothing was ever too clear.
And in mutual time trouble, it was Hans who faltered first, overlooking a nasty tactical shot. With just seconds on the clock, Sam found the winning sequence, forcing Niemann to part ways with his rook for just a bishop.
After that, it always seemed like a long shot that Hans would survive. And while it wasn't an easy conversion, Sevian was pretty clinical.
In the end, it was Sevian's day, who leapfrogs Niemann in the standings and ends the round in 4th place, with a very real shot at a podium finish if he can find a way to win against Ray Robson in tomorrow's final round.
Niemann looking for a podium finish
It all started very well for Hans, but back-to-back defeats in rounds 7 & 8 (to Caruana and Woodward respectively) effectively ruled him out any chance of clinching what would be his first U.S. Championships title.
Still, with just two rounds to go, he's performing respectably with 5/9. A strong finish in the final two rounds would give him excellent chances at a podium finish, which would be a very solid result in a stacked field like this one.
Sam Sevian however, has also shown that he belongs among the elite. He's scored 50% so far, and he might just come into today's game feeling that this is as good of a chance as he's going to get to build upon this and finish 'on a plus score', as chess players say when they speak of tournaments where they scored more wins than losses (not counting draws).
Hans of course, is always ambitious. So I doubt we're going to see these two young players trying to kill the game early. Or at least, let's hope not!