In the winter of 1977, in Reykjavik, Iceland, Vlastimil Hort, a Czech grandmaster ranked No. 6 in the world, was facing off against Boris Spassky, the Russian former world chess champion who had lost to Bobby Fischer in the same city five years earlier.

The match was a best-of-12 quarterfinal, whose winner would be one step closer to the top title in chess. After 12 games, they were tied, prompting a two-game playoff.

Then Mr. Spassky fell seriously ill. He was taken to the hospital, and his appendix was removed. According to the rules, he was entitled to three postponements of three days each. He took them all, but was still too unwell to play.

Mr. Spassky would have to forfeit, meaning Mr. Hort would advance to the semifinals.

Then Mr. Hort did something unexpected. To give Mr. Spassky a chance to continue to compete, Mr. Hort requested a three-day timeout, which was granted. It was a choice seen for decades as one of the greatest acts of sportsmanship in the history of the game, and it ended up costing Mr. Hort the match.

By the end of the timeout, Mr. Spassky could resume play, and after Games 13 and 14 were drawn, another two-game playoff was needed. In Game 15, Mr. Hort reached a winning position, but he froze. His time expired before he had made the required number of moves, thus forfeiting the game. After the next game ended in a tie, Mr. Spassky was declared the winner of the match.

Mr. Hort lost his chance to play for the world championship and never qualified again.

He died on May 12 at his home in Eitorf, Germany, near Bonn. He was 81. His wife, Brigitte Hort, said the cause was complications of diabetes, for which he had been treated for 30 years.