VIENNA, SEPT. 23 -- Like the boy who stood on the burning deck whence all but he had fled, American Michael Chang rallied to keep U.S. Davis Cup hopes alive with a third-set victory today over fired-up Austrian Horst Skoff before darkness postponed the conclusion of their match.

The match will resume Monday on a clay court at the Prater soccer stadium with Skoff leading Chang, 6-3, 7-6 (7-4), 4-6. With the series tied at two matches each, the winner puts his team in the finals Nov. 30-Dec. 2 against Australia, which defeated Argentina, 5-0.

Chang, 18, was put in the do-or-die role after Andre Agassi lost to Thomas Muster, 6-2, 6-2, 7-6 (7-2), in the first of the day's two rain-delayed matches. The Austrian, ranked seventh in the world, extended his Davis Cup record on clay to 24-0.

Muster, who tossed his racket in the stands after winning, said the flag-waving crowd of 18,000 -- including President Kurt Waldheim -- bolstered him. "All the crowd, it just gets into you," he said. "It must be one of the best matches of my career, certainly perhaps the most important for Austria."

Skoff, 22, picked up the mood, jumping to an early lead over the tentative Chang. Using a powerful cross court forehand, Skoff broke Chang's two first service games and won the first set in 37 minutes.

Chang broke Skoff for a 4-2 lead in the second set. But Skoff broke back at love in the next game and, serving strongly, won the tiebreaker, 7-4.

That put Chang, and the United States, one set away from defeat in the best-of-five semifinal, now tied at 2-2. The United States has won the Davis Cup 28 times, but has not been in the finals since 1984 against Sweden, and has not won since 1983 against France.

In the 56-minute third set, Chang's game picked up pace. He broke Skoff in the third game with a driving forehand down the line. After a grueling 25-stroke rally left the final game at deuce, Chang hit another winning forehand and Skoff's final shot went long.

Umpire Raymond Dombrecht ruled it was too dark to begin another set.

Austrian captain Filip Krajcik said the overnight break will benefit Skoff, who was fatigued and beginning to miss shots wide and long as Chang's methodical game came into focus.

Agassi, 20, was gracious in defeat. He praised Muster, 22, as a "class player" who deserved to win.

After losing meekly in the first two sets, Agassi, who had 58 unforced errors to 33 for Muster, pushed the third set to a tiebreaker. Muster won the tiebreaker and the match.

"It was just nerves, it was just something I felt," Agassi said. "I think all the cheers when I missed my first serve might have helped him. Next time we play, hopefully it will be some place outside Austria."

Agassi called the loss more personally disappointing than either his French or U.S. Open finals defeats. "In a Grand Slam final," he said, "the only person you let down is yourself. Here you have your entire country back home watching."

Three world group qualifying pairings ended, with the winners going for the '91 Cup and losers going through zonal qualifying. In Split, Yugoslavia, Goran Ivanisevic defeated Claudio Mezzadri of Switzerland, 6-1, 6-4, 6-2, to clinch for Yugoslavia before Switzerland's Marc Rosset beat Goran Prpic, 6-4, 7-6 (7-2), for the 3-2 final.

Stefan Edberg and Jonas Svensson gave host Sweden a sweep of Finland. Edberg beat Veli Paloheimo, 3-6, 6-4, 6-0, and Svensson topped teenager Aki Rahune, 6-4, 6-0. In London, Henri Leconte beat Jeremy Bates, 7-6, 6-0, and Guy Forget downed Cup rookie Nick Brown, 6-3, 6-2, to finish France's 5-0 sweep of Britain.