There were physical changes caused by the passage of time, but chess master Bobby Fischer behaved much as he had during his earlier period of fame. Bearded and heavier than he was 20 years ago, the American chess master emerged from two decades of seclusion last week with several of his old trademarks -- brilliant play and outspoken views -- still clearly evident. Before beginning a historic rematch with his old rival, 55- year-old Boris Spassky, in the Yugoslav resort of Sveti Stefan, Fischer, 49, denounced current world champion chess players. He also spat on a letter from the U.S. Treasury Department warning that his match was a breach of the UN embargo against what remains of Yugoslavia. Then, in the opening game of the chess match, which Fischer won in 49 moves over six hours, the American showed that the years had not dulled his ability. Said Lawrence Day, a Rexdale, Ont.- based international chess master who read press reports of the game: "Spassky played one of the lines that was his favorite when he was a world champion, so it's not surprising Fischer was prepared for it 20 years later."

The stakes are high. The winner will receive a $4-million prize and the runner-up gets $2 million. The lucrative match against Spassky, a former Soviet champion who now lives in France, was arranged and sponsored by Serbian banker Jezdimir Vasiljevic, who put up $6 million in prize money. In their second game, the two men agreed to a draw after 6½ gruelling hours of play. Their third game, on Saturday, also ended in a draw.

The match marked the return to international competition of a controversial chess genius who rose to prominence in 1972 -- and soon faded mysteriously from view. An intense former child prodigy from Brooklyn, N.Y., Fischer played brilliantly to defeat Spassky at the world championships in Reykjavik, Iceland, in 1972. The matches, played at the height of the Cold War, took place amid intensive security arrangements by U.S. and Soviet officials. At one point during the championships, Soviet security men even insisted on dismantling Fischer's chair to see if it contained secret electronic equipment to enable him to have expert counselling from hidden advisers. They found nothing.

In spite of its bizarre political overtones, the Reykjavik match featured brilliant chess playing. Fischer's victory gave the United States the world chess championship for the first time ever, and the brilliance of both players sparked an international revival of popular interest in chess. In Sveti Stefan, Yugoslavian grand master Srecko Nedeljkovic said of the match 20 years ago: "It was probably one of the best world championships ever."

Fischer lost his title three years later, when the International Chess Federation in Lucerne, Switzerland, took it away after he refused to defend the title against Russian Anatoly Karpov. Fischer said at the time that he felt that he had not been offered enough money. After that, he appeared to become increasingly eccentric. Living an elusive existence in California, he made few public appearances. During a four-month period in 1981, Fischer played 17 games of chess with Greek-born grandmaster Peter Biyiasas in San Francisco -- and won them all. Biyiasas told reporters later that while they were playing, Fischer carried around suitcases filled with mysterious pills from China and Mexico. Biyiasas said that Fischer told him: "If the Commies come to poison me, I don't want to make it easy for them." According to a former chess associate, Fischer, during the same period, had all his dental fillings replaced because he feared that Soviet agents might be able to transmit damaging rays into his brain through the metal in his teeth.

In Sveti Stefan, Fischer behaved at times as though he was still the world champion of chess. Before the match, he claimed that he wanted to compete against Karpov, who currently is rated as one of the world's top chess players, as well as Gary Kasparov, the current world champion. (Kasparov is a native of Azerbaijan, a former Soviet republic.) Fischer, who was accompanied by Zita Rajcsanyi, a 19-year-old Hungarian chess star, declared that he is currently working on a book about a series of world championship matches between Karpov and Kasparov during the past eight years. By defeating Karpov in 1985, Kasparov became world champion. Describing Karpov and Kasparov as "the lowest dogs around," Fischer charged, without giving any explanation, that their matches were rigged.

The Fischer-Spassky tournament could be a lengthy and unpredictable affair. It is scheduled to move inland to Belgrade, the Yugoslav capital, as soon as one player has won five games. But chess experts noted that in the past, Fischer had often dropped out of tournaments unexpectedly. Win or lose, Fischer could pay a stiff penalty just for taking part in the match on Yugoslav soil. Under U.S. law, the chess master could face up to 10 years in prison or a $250,000 fine for ignoring American-supported United Nations sanctions against Yugoslavia.