Leader Viswanathan Anand [Images] was stunned in the sixth round by old rival Gata Kamsky, in a major upset at the Corus Grandmasters chess tournaments in Wijk Aan Zee, the Netherlands.

But the Indian ace, despite the defeat continues to have a share of the lead with Veselin Topalov, while Kamsky shares the last place with Etienne Bacrot.

Anand, the NIIT [Get Quote] Brand Ambassador, is in shared lead with Toplaov, both having four points each from six rounds.

Kamsky, who has beaten Anand in the past, was in last place, while Anand led the tournament, when they clashed and they stayed there even after the India's defeat.

Kamsky played a clean game and did not give Anand any counterplay. He chose 1. d4 in Queen's Gambit Accepted and went for a side line with 9. Ne4 to avoid a duel in any main lines. Anand on the other hand decided to risk it and play for a win and it included a queenside castling on tenth move.

Kamsky strengthened his centre and then Anand allowed him to open the f file. Anand traded queens to get some play, but in the endgame with the weak e-pawn and also White's control of f file, it became an uphill task for Anand. He did get into a Bishops of opposite color but was a pawn down. Kamsky took a full point to give himself a chance to finish somewhere higher up in the tournament.

Shortly after Anand lost Michael Adams beat Vassily Ivanchuk in 44 moves of a Sicilian Scheveningen. Adams got a comfortable opening and gradually forced Ivanchuk into a passive position.

Sergei Tiviakov drew with Veselin Topalov in 61 moves of a Sicilian Alapin, while Ivan Sokolov and Peter Leko drew in 31 moves of a Queens Indian Petrosian System.

Shakhriyar Mamedyarov split points with Boris Gelfand in a Queens Indian. Etienne Bacrot drew with Levon Aronian in 29 moves of a QGD. Loek Van Wely and Sergey Karjakin played a marathon 80 moves in the final game for yet another draw as five games were drawn and two produced results.

In Group B, young Magnus Carlsen is on top of group B with an impressive five out of six.  India's Koneru, Humpy lost to Erwin L'Ami in 62 moves of a King's Indian.

Pairings for Round 7: Topalov v Sokolov; Gelfand v Tiviakov; Karjakin v Mamedyarov; Aronian v van Wely; Ivanchuk v Bacrot; Anandv Adams; Leko v Kamsky

Results of Round 6: Mamedyarov drew with Gelfand; Sokolov drew with Leko; Bacrot drew with Aronian; Kamsky beat Anand; Adams beat Ivanchuk; Tiviakov drew with Topalov; Van Wely drew Karjakin

Standings after Round 6: 1. Anand and Topalov 4.0 each; 3. Adams, Gelfand, Ivanchuk, and Karjakin 3.5 each; 7. Mamedyarov, Aronian 3.0 each; Leko, Tiviakov, Van Wely and Sokolov 2.5 each; 13. Kamsky and Bacrot 2.0 each.

• Complete chess coverage