Indian Grandmaster R Praggnanandhaa crashed through the defenses of compatriot Vidit Gujrathi but D Gukesh suffered a shock defeat from a position of strength against Czech Republic's David Navara in the fifth round of the Prague Masters in Prague.
Uzbekistan's Nodirbek Abdusattarov continued with his dream run and ran over Mateusz Bartel of Poland to emerge as the sole leader ahead of Parham Maghsoodloo of Iran, who played out a draw with Hungarian turned Romanian Richard Rapport.
In the other game of the day, local hopeful Nguyen Thai Dai Van played out a draw with Vincent Keymer of Germany.
With just four rounds to come in the super tournament, Abdusattarov sits pretty on four points out of a possible five and the Uzbek has in fact broken in the top five of world rankings now.
Maghsoodloo is now half a point behind on 3.5 points followed by Rapport on three. Praggnanandhaa walked his way back on 50% score at the expense of Gujrathi and shares the fourth spot with Navara and Gukesh.
Dai Van, Keymer and Gujrathi come in next on two points apiece followed by Bartel who has a single point in his kitty.
Gujrathi was up against an English opening and equalised without much ado even though the complications remained.
Praggnanandhaa, who is never short of ideas no matter what the position is on board, kept pushing for more in the middle game but Gujrathi was also up to the task in finding the right path.
The pieces changed hands and the players arrived at a Queen and rook endgame with resources for both sides, before Gujrathi fumbled and allowed a devastating attack against his king. Praggnanandhaa won in 52 moves.
Gukesh had what looked like an extra healthy pawn in the endgame and had little to worry.
However, the Indian was clearly not having a good day in final phase of the game as Navara pushed for some counterplay.
As it happened in the game, first the advantage slipped, then it was handed over to Navara which the Czech star converted after some hard-work.
Abdusattarov made quick work of Bartel in just 28 moves. The Uzbek made his intentions clear by going for the Sicilian dragon and clearly the Polish Grandmaster was short on ideas. It was an optical illusion as Bartel set out for a King side play but the damage was quicker on the other flank.
In the Challengers section Grandmaster R Vaishali went down to Erwin L'Ami of Holland and stayed on two points.
Meanwhile in the Shenzen Masters being held in China Arjun Erigaise came up with a super effort to down Anish Giri of Holland.
Results round 4 (Indians unless stated):
R Praggnanandhaa (2.5) beat Vidit Gujrathi (2.5); Parham Maghsoodloo (Iri, 3.5) drew with Richard Rapport (Rou, 3); D Gukesh (2.5) lost to David Navara (Cze, 2.5); Nguyen Thai Dai Van (Cze, 2) drew with Vincent Keymer (Ger, 2); Mateusz Bartel (Pol, 1) lost to Nodirbek Abdusattarov (Uzb, 4).
