Former world chess champion Anatoly Karpov took a long step yesterday toward winning back his title. Not only did he win Game 5 of his hotly contested match in Seville with defending champion Gary Kasparov, but he showed what looked like strong psychological leverage against his opponent.

For the second time in the last four games, Karpov surprised the champion with an unexpected departure from established strategy, and for the second time Kasparov blundered after getting into serious time trouble, this time leaving himself with only one minute to make seven moves. Two serious time gaffes only a few games apart may indicate some psychological distress that keeps the champion from concentrating totally on the game.

Karpov won his advantage by using an unfamiliar response in a familiar opening. Kasparov's first reaction was merely a raised eyebrow at a move that had been tried, found harmless and abandoned by leading grandmasters back in the 1950s. But then he spent 64 minutes deciding what to do with his queen on his 14th move. If Karpov can continue to surprise him with that kind of effect, it will not matter much whether they are improvements on previous tactics. Winning so much time from the opponent can be as valuable in championship chess as winning an advantage in space or material.

For two or three moves, Game 5 looked like a tame rerun of Games 1 and 3, which had threatened to give the Gru nfeld Indian Defense a reputation for dullness. Once again, Karpov had the white pieces, once again he opened with his queen's pawn, and once again Kasparov played the characteristic move of the Gru nfeld, 2. g6. Another odd-numbered game, another Gru nfeld. Another tame draw seemed in the offing.

Now, one has to wonder whether Karpov made those earlier games so uneventful as part of a long-term match strategy to lull his opponent into false expectations. In any case, Game 5 soon exploded into carnage. This was not the sedate Four Knights Gru nfeld but the action-packed, dangerous Exchange Variation -- the first time Karpov has played it against Kasparov in more than 100 games.

Pieces that had crouched timidly behind impregnable stone walls in previous Gru nfelds charged boldly into action. Some were cut down, but they fell fighting. Unlike the fearful symmetry that hung over the match's two previous Gru nfelds, the position this time became perilously unbalanced.

For a half-dozen moves, the opening followed a course familiar from textbook games. Then Karpov uncorked his surprise move: 12. Bxf7 ch -- not a new idea; in fact, one that predates Kasparov's birth. So old, it might as well be new. Presumably, Karpov had some new wrinkles for various possible sequences following this dramatic smash-and-grab. The variation led into sharp, double-edged play but not necessarily a disadvantage for Kasparov. In exchange for a lost pawn, he controlled the most important squares on the board, and his pressure on the queenside eventually forced Karpov to surrender his extra pawn.

Kasparov began creating what looked like the beginning of a deadly assault, but Karpov gritted his teeth and held on tight, fending off threat after threat. Finally, under extreme time pressure, Kasparov must have been carried away by his aggressive enthusiasm. He was threatening checkmate (for example, 38. Rxa1, Qxg4, mate) if he could remove the white rook that was guarding the g-pawn. But in his zeal to achieve some variation of this simple yet deadly coup, he overlooked the fact that Karpov, with his 37th move, Qxa6, was preparing a direct hit on the black king.

That capture with check completely transformed the double-edged situation. Previously, Kasparov's rook on a1 had been cleverly placed; Karpov could not capture it without suffering instant checkmate. But after 38. Qxpch, Karpov had not only gained a vital tempo, but his queen was positioned to guard the crucial pawn on g4 and to gobble Kasparov's rook at his leisure. The champion's position disintegrated completely.

The match score is now 3-2 in Karpov's favor. The winner of the 24-game contest will be the first player to score 12.5 points or achieve six victories. A win scores one point and a draw scores a half point. In the event of a 12-12 tie, Kasparov will retain his title.

The sixth game is scheduled Monday with Kasparov playing white.

Grandmaster Lubomir Kavalek contributed to this report.