After yesterday's games four players were one draw away from advancing to the quarter-final round of the 2015 World Cup: Peter Svidler, Hikaru Nakamura, Shakhriyar Mamedyarov and Ding Liren, who defeated Veselin Topalov, Michael Adams, Fabiano Caruana and Wei Yi, respectively. After today's games, four players have indeed qualified for the quarters, but only three of the four come from the aforementioned quartet.
Svidler was getting outplayed by Topalov in an Anti-Marshall, but shortly before the time control Topalov let the advantage slip. Worse still for the Bulgarian's fans, his first two moves in the second time control were serious errors, and only the fact that there was still one line at the end where Topalov could at least cause a tiny bit of trouble - a rook down - if Svidler declined the draw offer prompted the Russian to settle for a 1.5-.5 match win.
Nakamura's troubles, by contrast, were pretty mild. Maybe there was a move or two where Adams had a tiny something in a Berlin ending, but its solidity held up and Nakamura coasted into the 5th round.
Mamedyarov had a more serious disadvantage on the black side of an Open Ruy against Caruana, but the American's 24th and 25th moves turned out to too accommodating. With 25...Bd5 and especially 26...a5!! Mamedyarov obtained enough counterplay to save the game. Caruana may have thought he would enjoy a big advantage after 26.Bxb5 axb4 27.e6 fxe6 28.Bxc6 Bxc6 29.Ne5, but the ice-cold 29...Bd6! 30.Reg3 Rd7! held everything together. After that the only player with an edge was Mamedyarov, but the draw sufficed and the players repeated moves until splitting the point at the time control.
That leaves Ding Liren, and the obvious implication that he was defeated in the second game of his match with Wei Yi. Wei Yi outplayed his opponent in another Anti-Marshall (by transposition) and won a pawn, but converting it proved to be exceedingly difficult. Once they reached a rook ending, both players - Wei Yi especially - were quite short of time, and as it was a complex ending both players made errors that could have cost first one and then the other half a point. Ultimately, the practical task facing Ding Liren was too difficult, and his 72nd move lost by force. I suspect that his position was practically hopeless in any case, at least without a lot of time on the clock. Tomorrow, both he and his opponent will have even less time if and when they reach a similar ending; they're headed to tiebreaks.
Someone who is not headed to tiebreaks: Maxime Vachier-Lagrave. (Also his opponent, for that matter.) MVL found himself in a lousy position out of the opening, but Wesley So came up with a very clever combination that was, sadly, too clever by half. The tactical sequence that began with 22.Bxd5? (and was perhaps envisioned on the previous move, which was also inaccurate) came a-cropper when Vachier-Lagrave played 26...Bc6. After that So fought long and hard for a draw, but couldn't quite pull it off. (The subtle 41.Ra7 was his last, best chance to save half a point, with the idea that if Black takes on f2 a series of checks will eventually force Black to cough up his g-pawn. Instead, 41.Rf6 allowed Black to lock up his remaining kingside pawns in a way that guaranteed that the h-pawn would survive and that Black could swap off the rooks.)
The other three matches saw draws and will see tiebreaks. Radoslaw Wojtaszek had an advantage against Anish Giri, but didn't manage to turn his space advantage into something more tangible. Pavel Eljanov played 60 moves against Dmitry Jakovenko, enjoying a slight advantage the whole time, but never came even a little close to getting anything serious. Finally, Sergey Karjakin and Dmitry Andreikin played on a little longer than they did yesterday, but it was always clear that they were headed for a short day and tomorrow's tiebreaks.
Interestingly, none of the round 5 matches are settled, as all of the round 4 winners must wait for tomorrow's tiebreakers to determine their opponents.