Victor Korchnoi lost two games in one afternoon, and suddenly the neck-and-neck world chess championship match looked like a runaway victory for the defending champion Anatoly Karpov. The afternoon began with the match score tied at 1-1 and ended with Korchnoi trailing by 3 to 1. The championship and a prize of $350,000 will go to the first player who wins six games; the loser's purse will be $200,000.

Both of the games lost by Korchnoi were continuations of games: Game 13, which was begun on Thursday and game 14 which was began on Saturday. According to the orginal schedule, game 13 would have been continued on Friday, but Korchnoi asked for a postponement - thus setting himself up to be the first player to lose two games in one day in a world championship match.

The loss in game 14 was not totally unexpected. On Saturday, Karpov secured a winning advantage with a precisely-timed sacrifice of the exchange (rook for bishop and pawn) on his 29th move, and he went into the Sunday session with two passed pawns and his pieces well placed. But before getting to game 14, the players had to finish game 13, and in this one Kirchnoi seemed to have a winning advantage.

Korchnoi's sealed move in the first game (over which he had pondered for 40 minutes, putting him in time trouble for the whole second session) was the highly aggressive 41. R-R7, which led to a reduction of the forces on the board. His 43, P-Q5 cleverly exploited the immobilization of the black rook to win a pawn (43. . . . PxP; 44. BxP would have led to the loss of the pinned rooks), but the extra pawn proved useless in the rest of the game.

Karpov defended his shaky position brilliantly, mobilizing an attack that kept his opponent off balance, and finally Korchnoi blundered with his 56th move, isolating his queen out play at the side of the board and allowing Karpov to generate a mating attack. In the final position, Korchnoi's pieces were immobilized and he had no useful defense against Karpov's threat of 62 . . . B-R4ch.

After Korchnoi's blunder on his 56th move, Karpov caught the scent of victory, stood up, walked to a corner of the stage and fixed a contemptuous stare on his opponent. Then he went back to crush his position.

After a 30-minute rest period, game 14 was resumed and Karpov won it in nine moves which required only 45 minutes. The victory in this game was a matter of pure technique, but Korchnoi, evidently shaken by his first loss, made it easier for his opponent. Some of his moves look almost as though he was in a hurry to end the ordeal; for example, 48. . . . R-QRI rather than the ineffective . . . R-QBI might not have saved the game, but would have made Karpov's job more complicated.

In the final position of game 14, Korchnoi is in check and cannot move without losing his rook and allowing Karpov to make a queen immediately after.

According to observers in Baguio City, The Philippines, Korchnoi seemed shattered when he lost the second game and hurried from the hall. But yesterday's loss was not the most spectacular he has suffered in his drive for the world chess championship. In his challenger's match with former champion Boris Spassky, after piling up a five-point lead, he lost four games in a row, then recovered and went on to win the match.

He will have until tomorrow afternoon to pull himself together for game 15, in which he will play white.

After the second defeat, British grandmaster Michael Stean, one of Korchoi's seconds, summed up the challenger's feelings: "A 3-1 lead means very little, but the psychological blow in losing a good position is another thing."