The Chebanenko Slav (4...a6) is notoriously hard to beat. Dmitry Gurevich (who really really wanted to win tonight!) opted for a slow positional squeeze, and came close to converting against fellow GM Julio Becerra. The match situation required Becerra to play for a win to tie the match, and he found a good move (35...f5!) in mutual time pressure.
Dmitry still would have been better if he had played the consolidating move 36.Be3: 36.Kh3? was just too risky. Even in the game, 39.Qb1! kept the pressure on Black.
41.Bxf4? lost by force: kibitzers pointed out that Dmitry probably rejected 41.Qb7!? because it doesn't really threaten anything: the Re8 covers the back rank, and the Ng5 and Bd4 protect the sensitive squares in front of the Kg8. But the queen-rook battery on the seventh would have tied down several Black pieces to the king's defense: for example, 41...Nxf3 allows 42.Qh7+ Kf8 43.Qh6+ with a perpetual check.
Easy for a computer!