Aronian opens the game up with the king's pawn, a move he has essayed often throughout his long career.
Caruana mirrors his move
He eschews the more aggressive terrain of the Sicilian Defense, instead keeping the symmetry early on.
Aronian steps his knight out, targeting the central pawn.
The first key moment
This move is noteworthy not because it's unusual; in fact it is the most popular path taken by the Black side. The reason it's an interesting moment is that when Caruana has wanted to play for a draw, he has in the past gone for the ultra-solid Petroff Defense. So the fact he did not do this suggests that he may be looking to keep winning chances alive....
Aronian goes for one of the most classical systems in chess, stepping his bishop out to pressure Caruana's queenside knight in what is known as the Ruy Lopez, or Spanish Game.
Caruana immediately targets the invader bishop.
Aronian drops back
Back in the day it was quite popular to play bishop takes knight (an old favorite of Bobby Fischer's). But these days computers have shown that there's absolutely no edge there for the White side, so it's fallen out of popularity.
Caruana develops his kingside knight, targeting the central pawn.
Aronian invites the capture
He shows he's happy to play the so-called 'Open Variation' of the Spanish, if Caruana decides to capture the pawn. The point si that Aronian will have such a big lead in development that it won't be difficult to quickly win his pawn back.
Caruana grabs the pawn to move into the somewhat forcing terrain of the Open Spanish.
Aronian pressures the central pawn
He's now threatening to win his pawn back, but Caruana cannot play pawn takes pawn here. Doing so would leave his knight far too exposed along the central file.
Caruana focuses on development
He ignores the pressure against his central pawn, focusing instead on getting ready to castle as soon as possible.
Aronian targets the knight
It's the most vulnerable piece in Caruana's position, so Levon turns his attention to it, while adding to his development.
Caruana kicks the bishop back.
Aronian ignores the attack!
Instead, he just chops off Caruana's knight, inviting some more piece trades. The players are following a line that Caruana himself has played on a handful of occasions.
Caruana takes a moment to target the rook, since capturing the bishop back immediately would have allowed Aronian the strong option of pushing his own queen's pawn forward and suffocating Caruana's pieces.
Aronian trades pawns in the center. This line, besides having been essayed by Caruana, has also been played several times from the Black side by Magnus Carlsen -- once even against Mr.Caruana himself!
Caruana trades off knights. Forced, since if he took the bishop back immediately then this piece would have been hanging.
Aronian stalled briefly, likely mulling over the possibility of the secondary option of playing bishop takes pawn with check. Ultimately though, he sticks with the most battle-tested continuation.
Caruana finally recovers his piece
Quite the messy position! Welcome to the age of super strong computers, that allow players to find unorthodox paths to equality with relative ease. Aronian has several interesting options to choose from here, with one of the ideas being to add to the pressure against the pinned bishop, while another is to pressure the central pawn by jumping forward with the knight.
The less traveled path
Aronian ultimately settles on a move that is a rarer guest. Though it's not going to bother Caruana. The idea here is generally to prepare to trade off bishops, and Fabi has already made it clear by going for this system that he will be happy with a draw today.
Caruana gets out of dodge
He couldn't afford to keep his king in the center much longer, while he's got no reason to worry about the threat of pawn takes pawn as that would leave Aronian's pawn chain in ruins.
Aronian opts for a really direct and relatively rare choice. On the one hand, I want to declare that this game is "for sure heading for a draw!" because of the forcing approach to simplifying the position that Levon has taken...
...but, the part that makes me feel like maybe we're going to be in for a tough battle, is that the endgame that results is very easy for the computer to play out to a draw, but deceptively tricky for human players.
Ultimately, the question is whether Aronian is playing in this way to finish the game as soon as possible today. Or whether he feels this is a good way of playing for a win while keeping his risk down.
The theory battle continues
Caruana is playing the sequence of moves very quickly. The point is that he's setting himself up to drive his light-squared bishop forward, by first pinning the pawn in front of Aronian's king.
Aronian recovers his rook
But now, Caruana doesn't have to immediately take the bishop back. He's got a clever move here that will force Aronian's queen to passively defend.
So far, Caruana is 'acing the theory test'! He sets up a threat of checkmate, that forces Aronian to go passive with his queen. Pushing the pawn forward instead would be a very bad idea, as it would leave his king a little too weak along the light squares.
Aronian covers against the threat
It's worth noting that Aronian couldn't have jumped forward with his queen, to both defend the pawn and hit Caruana's bishop. The reason is that that would have left his back rank fatally weak!
Caruana now takes the bishop back, with his king so that he maintains a bit more piece control over his fragile queenside pawns.
The knight jumps forward, and now the threat of taking the pawn becomes very much real, since Aronian's structure would no longer get damaged in the process.
Caruana takes, since he wants to keep the material equal.
How much more theory?
The players might both know three or four more moves from here, max. But it's likely that their preparation will soon be coming to an end. And so, we should soon know if Levon will have any clever ways of pressuring Caruana from here, or whether he's mostly played in this way to make a fast draw.
Still the top computer moves
It can sometimes be strange to commentate such games. There is a joke, where the student asks "why this move?". And the chess coach replies: "because it's the best move!". Caruana has been playing the top engine line throughout for a long time now.
Aronian offers a draw!
This move is a clear signal that Levon does not have any aggressive intent today. The reason is that this move invites Caruana to move his queen forward, which will force a drawing line by taking advantage of a hidden perpetual check.
A perpetual check refers to continuous checks that the defending side cannot escape, and will lead to a draw by 3-fold repetition (the same position repeating three times).
Caruana brings his queen forward, forcing a premature end to the game. The reason is that now Aronian has absolutely no good move besides playing knight takes pawn, but then there is going to be a forced draw!
Aronian initiates the drawing sequence
He takes the central pawn, forcing Caruana's hand to play bishop takes pawn in order to lock down the drawing sequence.
Caruana doesn't hesitate to take the pawn, evidently familiar with the key idea. The point is that if king takes bishop now, then Aronian would land in trouble after Caruana dropped back with his queen to give a check that would fork the knight.
Due to the fork, Aronian has no choice but to play queen takes bishop, but now there's a nice geometric idea that will secure the draw for Caruana.
Caruana begins with the check, forcing the rooks off the board and beginning the series of endless checks.
Aronian has no choice but to accept the trade of rooks.
Caruana takes back, forcing Aronian to drop back with his queen to block the check.
Aronian covers against the check.
Securing the draw!
This is the key check that Caruana is relying on in the sequence. Aronian can keep blocking, but Caruana will always be able to continue checking.
Aronian blocks the check
But the drawback is that now the back rank is weak, so Caruana can return to giving checks from the side.
Caruana returns to the scene of the crime, giving another check and forcing Aronian to once again return with his queen.
Aronian drops back once again.
Caruana returns to checking diagonally
It's possible for Aronian to block the check with his pawn, but that would not change anything as Caruana would still have the same idea of giving perpetual checks.
Aronian blocks the check once again, as we reach the final stages of the game.
Will Caruana secure his fifth U.S. title?!
It's the final round of what's been a long and exhausting tournament, and we come into it with the top seeded Fabiano Caruana with fate in his hands.
A win today would guarantee victory, while a draw would force Wesley So to win against Grigoriy Oparin in order to level the score and force a tie-break playoff.
A big area of speculation, to which there is no easy answer, is just how motivated is Levon Aronian going to be? On the one hand, a win would secure a top 3 finish for him. On the other, a draw is likely to have the same effect. And although he may have the benefit of the White pieces, his opponent is a tough nut to crack, as evidenced by the fact that Caruana has yet to suffer a single defeat in this year's tournament.
Levon would certainly shake everything up if he *were* to defeat Fabiano, a result that would open the doors for Wesley to leapfrog him in the standings with a win against Oparin. And certainly, given that Wesley has the White pieces, he will likely be optimistic about his chances to win.
In any case, let's put speculation aside for now. In half an hour, final round of classical games will get underway. And it won't be long until we discover just how aggressive of a mood these two players are arriving in!