What an eventful round! After two rounds (and three rounds out of four) with only draws, today there were two wins, and both of them saw the winners catch Fabiano Caruana in first place.
Had Caruana won his last round game against Wesley So, he'd have taken clear first. The game was a staid Petroff, and though Caruana obtained a tiny edge with Black it was nowhere near enough to achieve anything serious, and the game finished in an uneventful draw. That guaranteed Caruana at least a tie for first, but four other players - two of whom faced each other - had the opportunity to catch him in the lead.
Levon Aronian and Alexander Grischuk both entered the round half a point behind Caruana, so if either player beat the other they'd tie for first. An equal but unbalanced position went completely out of control when Aronian offered a gutsy semi-bluff of a rook sac on move 18. Grischuk was relatively short of time even before the sac, and never managed to consolidate his material advantage. He'd alternate, making a series of good defensive moves followed by the occasional error, and after a total of three errors he was lost. Fortune favored the brave, and Aronian caught Caruana.
Magnus Carlsen was also rewarded, but not so much for bravery as for doing his thing. He had a slight advantage against Hikaru Nakamura, and while the position was objectively drawn Carlsen had nothing to lose and everything to gain by continuing to try, and eventually it paid off. It has to be said that Nakamura's 62nd and 66th moves were very strange. My guess is that he believed the setup he went for was drawn, and was therefore willing to burn all his bridges to head for it. Considering that the position prior to those decisions was only barely worse and had a big margin for error, this was a needlessly risky decision. As it turned out, he missed something, and the result was a technical win that Carlsen successfully executed. That made it a three-way tie for first.
If Shakhriyar Mamedyarov had managed to defeat Viswanathan Anand with the black pieces it would have been a four-way tie. But this wasn't going to happen. Anand enjoyed a slight edge in a very theoretical line of the Open Ruy, and Mamedyarov was never going to do more than work his way to a draw after some suffering - which is what happened.
Finally, in the one game that didn't matter in the race for first, Sergey Karjakin barely avoided a fourth loss in the tournament when he held a rook ending two pawns against Maxime Vachier-Lagrave. (Today's games, with my notes, are here.)
Will there be a playoff tomorrow? Yes...but not to settle the race for first. The rules called for a three-way tie to resolved by a drawing of lots to eliminate one of the players, followed by a playoff involving the other two. Apparently Carlsen was less than thrilled with this idea, and proposed either a three-way playoff or shared first. As I understand it, the other two players were on board with Carlsen's rejection of the scheme presented in the rules, but one of the two was against the playoff and preferred the shared crown.
My guess is that the objection came from Caruana, and with good reason: he's already committed to a playoff against So for the fourth and final slot in the Grand Chess Tour final. Therefore the three leaders are also the three champions, each of them a repeat champion. Here are the final standings from the tournament:
1-3. Aronian, Carlsen, Caruana 5.5 (out of 9)
4. Mamedyarov 5
5-7. Grischuk, Vachier-Lagrave, Anand 4.5
8. So 4
9-10. Karjakin, Nakamura 3
And these are the final overall standings for the Grand Chess Tour:
1. Nakamura 34.5
2. Aronian 34
3. Vachier-Lagrave 31
4-5. Caruana, So 26
6. Karjakin 25.5
7. Mamedyarov 25
8. Grischuk 18
9. Anand 15
The Caruana-So tie will be settled by a pair of 25'+10" games, and if it's still tied there will be up to three pairs of 5'+3" games. After that, the arbiter and the players will decide on another way of resolving the tie (presumably an Armageddon game, but who knows).