It all came out in the open Thursday night -- the tension, the emotion, the festering rivalry between the world's two greatest chess players, now locked in their second battle for the world title.

Until then, champion Anatoly Karpov and challenger Gary Kasparov had stuck to a script of cool, perhaps frosty, correctness. At least three nights a week for the past two months, the two have taken their places in the giant Tchaikovsky Hall and silently played out their antagonism on a board with 16 pieces for each.

Thursday, Kasparov, 22, took a decisive lead in game 19, a game that may well go down in chess history as the one that made him the youngest world champion ever.

This morning, faced with inevitable defeat, Karpov resigned the game, which means Kasparov now leads by 10 1/2 points to 8 1/2, with five games remaining.

Not only did Kasparov have Karpov in a corner, but he put him there with a grand and defiant gesture that, once again, made the tall, dark and handsome chess genius from the southern city of Baku a perfect fit for the role of the brash, arrogant young challenger.

For his part, Karpov, who at 34 has spent almost a third of his life -- 10 years -- as world champion, also followed central casting's cue by seeming to retreat behind his title, conceding only with great difficulty that he can be outplayed.

In short, Thursday night recaptured some of the touches that turned the conclusion of the last match between Karpov and Kasparov into a highly dramatic fiasco. It also proved that the bad feelings and murky politics of those days in February still haunt the chess world.

According to a recapitulation by experts today, both players got caught in a time scramble after more than four hours of play, and in the ensuing war of nerves, Karpov blundered. Faced with what many considered to be an overwhelming disadvantage, the champion refused to resign, an intransigence considered by some to be a breach of chess protocol.

Visibly exasperated at the end of the game's 40th move, Kasparov sealed his next move in an envelope. But rather than let it lie there until morning, he elected to play it out publicly on the board. The gesture, besides showing Kasparov's flair for the histrionic, also showed his contempt for Karpov's weakened position.

"It was a good psychological move," said David Goodman, an international master. "It leaves Kasparov in an obviously dominating position."

As the game drew toward its dramatic conclusion, the seats in the brightly lit concert hall filled up. Spectators, holding some of Moscow's most sought-after tickets, left their caviar sandwiches at the buffet and their chess games in the hallway to watch the excitement.

In the "grandmasters room," where the sultans of chess hold court while whisking through variations of the championship moves seen on a video screen above their heads, an excited throng gathered expectantly.

According to those present, when Kasparov played out his final move a roar of approval went up in the hall. "It was like a basketball game," said one observer.

According to another, an enthusiastic Kasparov supporter was even ejected from the hall for calling out for Karpov's resignation after the champion failed to announce it.

Most agreed today that the game may well be the turning point. Kasparov, who had already jumped ahead a point in the 16th game, has now established a lead so commanding that Karpov supporters are coming up with theories to justify a Kasparov win.

"One key element here is psychology," said Eduard Gufeld, a grandmaster, match official and Soviet chess trainer. "Kasparov's psychology is very good."

According to Gufeld, Karpov is still recovering from seeing his lead of 5 to 0 in the first championship match slip away, only to be faced with a brand-new match seven months later.

At the end of that 48-game match last February, Karpov still led, 5 to 3, but he had not won any of the last 21 games. The match had switched to a defensive duel as the robust Kasparov bore down on the slighter, frailer Karpov, winning both the 47th and the 48th games.

A haggard Karpov later insisted he wanted to continue playing, but the match was called off by officials for the publicly stated purpose of protecting the health of both players.

At a highly charged press conference, an outraged Kasparov challenged the chess establishment to explain why his chance to win was being taken away. This summer, he gave interviews to Yugoslav and West German magazines, speaking more strongly against what he perceived as favoritism shown to Karpov.

Although the two players shake hands at the end of each game, Kasparov has refused to talk to Karpov, at least twice turning away conversational gambits offered by the champion to discuss the complexity of a game.