With a marathon win against Vladimir Kramnik, world No 2 Shakhriyar Mamedyarov surged to the top spot, which he shares with Fabio Caruana, at the Candidates Tournament in Berlin.
Mamedyarov beat the Russian world No 3 in 70 moves to top the standings after the sixth round.
Caruana drew with Russian GM Alexander Grischuk to retain the top spot in the standings. Meanwhile, Wesley So beat Levon Aronian to clinch his first win of the tournament.
Kramnik and Alexander Grischuk and Ding Liren are tied on three points, while Levon Aronian and Wesley So are at 2.5. Sergey Karjakin, who drew with Liren in the six rounds, has two points.
With eight more rounds to go in the tournament, which will decide the challenger to face Magnus Carlsen for the world championship, more twists can be expected. But based on the performances so far, Caruana, 25, and Mamedyarov, 32, appear to be in a strong position.