Challenger Gary Kasparov defeated champion Anatoly Karpov today for his third victory in the world chess championship, making the overall score 5 to 3 after 48 games in the record-breaking series.

It was the second loss in a row for Karpov, who still needs only one more win to retain the title he has held since 1975. The next game is scheduled for Monday, with Karpov playing the white pieces.

Karpov, 33, who has not won a game since he established a commanding 5-0 lead on Nov. 24, appears to be showing the effects of the grueling marathon, already the longest in history and now entering its sixth month.

Kasparov, 21, defeated Karpov in 67 moves, brilliantly parrying all defensive tricks the champion threw at him.

The 48th game had been adjourned Friday after 40 moves and continued Saturday. In the adjourned position, Kasparov had a king, a rook and five pawns to a king, a rook and four pawns for Karpov.

When play resumed, Karpov tried twice to sacrifice his remaining rook to get a so-called "fool's mate" draw -- a situation in which the king is not under attack but no legal move is possible.

But Kasparov wouldn't fall for it. When he evaded the fool's mate trap twice and Karpov couldn't continue it, the champion resigned on the 67th move.

Karpov blamed his defeat yesterday on his concentration being upset by the shift of venue from the prestigious Hall of Columns in central Moscow to the Hotel Sport out in the suburbs, chess sources said.

Karpov has twice successfully defended his title, won in 1975 when American Bobby Fischer defaulted, both times against defected Soviet Viktor Korchnoi.