Victor Korchnoi, the Soviet defector, won his first victory in the world chess championship series Friday and had taken a slight advantage in the seventh game, which started during the weekend, against his arch-rival and current champion, Anatoly Karpov of the Soviet Union.
Experts said Friday's match was the best in the series so far. Korchnoi's first victory was considered essential for him to maintain any chance of winning the championship. Korchnoi is down 1 to 3 in the series. A player must win six games for the tournament. Draws don't count.