The grandmasters at Wijk aan Zee have been producing more than their fair share of blunders over the past few days. Nikolic, after securing a small but clear endgame advantage against Salov, pursued his opponent's king so relentlessly that he drove it into a winning position amongst his own Q-side pawns. Nigel Short also spoiled a potentially winning position against Granda Zuniga of Peru.

After tempting his opponent into a dubious piece sacrifice, Short, playing Black, reached the diagram a piece for two pawns up. He continued 1...Rc8?! (setting up the blunder that follows) 2.Nf5+ Kf8 3.Rg3 Rh5? (either Nh7 or f6 is necessary) 4.h4! Nh7 5.Rg8+! Kxg8 6.Nxe7+ Kf8 7.Nxc8 and White has a winning position.

The prize for the biggest blunder, however, must go to Illescas for the way he threw away his game against Yermolinsky.

In the diagram position, Black faced problems defending both his vulnerable king and his b7-pawn, but he really ought to have lasted more than two more moves. The game ended 1...Qg7 2.Qb1+ Qg6? 3.Rxf7+ and Black resigned.

Leading scores with four rounds left: Piket and Sokolov 61/2; Salov and Onischuk 51/2. Short, despite a ninth round win against Glek, trails in 11th place on 31/2.