Vishwanathan Anand suffered a second loss at the Corus Grandmasters Chess tournament and that dented his chances of sixth Corus title seriously.
Anand, who lost to Vladimir Kramnik in the sixth round, went down to Veselin Topalov in eighth round. Two losses to top players in the same tournament is a rarity with Anand.
The NIIT-sponsored Anand now has four points and is tied for seventh.
Topalov, with his win over Anand, took over as the new leader, as erstwhile leader Teimour Radjabov also suffered a loss at the hands of Lev Aronian.
Topalov has six points, Radjabov 5.5, while four players, Vladimir Kramnik, Lev Aronian, Peter Svidler and Sergey Karjakin have five each.
In Group C, Parimarjan Negi also suffered his second successive loss, going down to M Bosboom. He lost to Emmanuel Berg in seventh round earlier.
Negi is now tied for sixth with four points. Ian Nepomniachtchi leads with 7.5 points.
The Topalov-Anand game was in Queen's Indian, though Topalov claimed he had also prepared for the Slav. Anand moved away from 13 b5, a line Topalov faced last year and instead opted for 13..fxe4.
Clearly Topalov had expected it and his next move 14.a4 was to stop b5 and also create a threat. By now white (Topalov) had an edge. The next few moves were forced sequence and then by 20th, Topalov with b4 gained crucial advantage.
Anand realising he could not allow Topalov to quietly keep taking advantage launched his own plan to get counter play. But it did not work as he did not get counter play.
The Bulgarian was accurate in his further play and continued with 34.Qc5 and that resulted in Anand realising he had no chance and resigned though he could have continued for a while. But Topalov in his current form could not be expected to make mistakes at this stage.
Leader Teimour Radjabov suffered his first loss in a 65-move game against Lev Aronian in queen's gambit declined.
Results of Round 8: Topalov beat Anand; Radjabov lost to Aronian; Kramnik drew with Carlsen; Motylev lost to Svidler; Van Wely drew with Ponomariov; Shirov drew with Tiviakov; Karjakin beat Navara.
Standings: 1. Topalov 6.0; 2. Radjabov; 5.5; 3. Aronian, Karjakin, Kramnik and Svidler 5.0 each; 7. Anand and Navara 4.0 each; 9. Ponomariov 3.5; 10. Motylev, Tiviakov and Van Wely 3.0; 13. Carlsen 2.5; 14. Shirov 1.5.