Suddenly, as yesterday's world title session in Seville neared adjournment, chess champion Gary Kasparov was handed a clear shot at his third win over challenger Anatoly Karpov.

Karpov blundered in an exchange of pieces, and if Kasparov manages to capitalize on the error when Game 11 is resumed today, he will hold a lead in the 24-game match of 6 to 5 and an incalculable psychological advantage. Since he retains his title if the match ends in a tie, the one-point lead has an effect more like a point and a half. Karpov will have to play harder for wins and take more chances in the 13 remaining games of the match, while Kasparov can accept draws with more equanimity.

After five hours of play, Kasparov wrote down his 41st move, sealed it in an envelope and went off to his secluded villa to work over continuations with his team of analysts. In another villa, Karpov and his team began working frantically to find ways out of a tough situation.

Karpov blundered badly on his 36th move, losing a rook for Kasparov's bishop, and he now faces an uphill struggle trying to hold a draw. The challenger has an extra pawn, but it does not look very useful, being doubled -- blocked by another pawn of its own color. If analysis indicates that he cannot stop Kasparov from winning, Karpov may not show up to continue the game today.

Before Move 36, Kasparov had been sending clear signals to Karpov that he would be satisfied with a draw -- and Karpov had been eagerly pressing a small advantage in hopes of a win.

For the sixth time, Kasparov played a Gru nfeld Indian Defense -- the only opening he has used with black in this match. And for the fourth time in those six games, Karpov chose the Exchange Variation, which leaves him temporarily ahead by a pawn.

It may be that Kasparov has loved the Gru nfeld not wisely but too well. Over the years, he has lost several games to Karpov with this defense, including Game 5 of the current match, and, if he wins today, it will be his first Gru nfeld victory over the challenger. The victory, however, will have arisen out of the late middle game, not the opening.

The games of this match with Karpov playing white have amounted to an intense debate over the value of the Gru nfeld. Karpov clearly believes that white obtains an advantage, while Kasparov believes that black can neutralize white's attack despite white'sextra pawn.

For the first 14 moves, both players repeated previous games -- almost as though they were engaged in exercises to see whether their hands still remembered what they had done before. Then they began to use their brains. Instead of 15. e5, Karpov chose another move that allows him to keep control of certain important white squares. But the first real surprise of the game came when Kasparov offered a queen exchange with 16. ... Qc4 rather than trying to recapture the extra pawn. This decision was probably based on his experience in Game 9, when he took too many moves to recapture the pawn and allowed Karpov to consolidate his position. In this game, Kasparov was merely trying to prove that his position is so strong that he can afford to enter an end game a pawn down.

The players used only 18 minutes for their first 19 moves, indicating that even after they departed from the pattern of previous games they were still, for a few minutes, in territory that both had examined at their leisure.

One dramatic episode came on Moves 20 and 21 when Kasparov, having set up his blockade, moved his bishop around it and into the thick of action, just one move before Karpov was ready to close the exit by moving his pawn to g5.

The bishop's dash to d2 and then to a5, where it covered many vital squares in white's position, had a last-minute "cavalry to the rescue" air about it. So did Kasparov's brilliant, three-move rook sequence, after 37. Bc7, saving his e-pawn from the marauding bishop. The preservation of this pawn is one of the elements that give Kasparov strong hopes of chalking up a victory today.

But Kasparov's chances were given their biggest boost by Karpov's 35. Rc6, obviously a blunder. Until then, Karpov had a strong position, arguably the better one, and he could have played almost any other move -- 35. Bf2, for example. Not 35. Bxb6, however; after 35. ... axb6; 36. Rf2, Ra3, Kasparov would have a very dangerous initiative, actually forcing the slightly comic move 37. Nh1 if white doesn't want to lose a pawn.

Before Karpov's blunder, Kasparov showed he was content with a draw in the sequence of moves between 24 and 27 and again in Moves 29 and 30, when he shuttled his knight back and forth, repeating the same position.

Grandmaster Lubomir Kavalek contributed to this report