VIENNA, SEPT. 21 -- Andre Agassi took the sting out of a charged-up Horst Skoff, then toyed with him for two sets today to give the United States a 1-1 tie with Austria after the first day of their Davis Cup semifinal.

Thomas Muster used his power to overcome the finesse of Michael Chang in the opening match of the best-of-five weekend series.

Agassi won the last three points of a tiebreaker in the first set and captured 12 of the next 13 games as Skoff ran out of energy. He needed less than two hours to complete his 7-6 (7-3), 6-0, 6-1 victory.

Skoff did not win a single point on his own serve in the second set.

"I think a lot of Skoff's tennis was on emotion that first set and I felt like it was just a question of getting through it," said Agassi. "If I had lost the first set, I think he would have played like that for a little bit longer, but I'm not sure how long he would have kept that up."

In the other Davis Cup semifinal, Australia took a 2-0 lead over Argentina in Sydney. The semifinal winners will play for the title Nov. 30-Dec. 2.

Agassi and Skoff traded sharp passing shots and delicate drop shots in the tiebreaker until the eighth point, when Agassi recovered from a slip to take a 5-3 lead. He won the next point on Skoff's serve, then delivered an ace to finish the set.

"Andre was playing great tennis. I've never played somebody who could put me under pressure like that, never ever. There was nothing I could do," Skoff said. "If you don't put pressure on Agassi he makes you run like a dog."

Skoff dropped the last 11 points, causing many of the 17,000 fans to leave the Prater soccer stadium in disgust.

"I picked up my game after the first set and he slowed down a little," Agassi said. "I don't know if he got fatigued, but he tried so hard the first set and had nothing to show for it."

In the opening match, 23 was the unlucky number for Chang as he lost, 4-6, 6-2, 6-2, 6-4, in an intermittent rain.

Muster improved his Davis Cup clay court record to 23-0 by taking advantage of Chang's weak serve. The American was in trouble throughout the match, facing 23 break points overall.

Muster's victory sent red and white Austrian flags fluttering in the stands and brought fans, some with their faces painted red and white, to their feet.

"It took me awhile until I got used to everything," Muster said. "The last three sets I was playing some of my best tennis."

The Austrian left-hander, ranked seventh in the world, did not lose his serve in the second or third sets and recorded four of his eight service breaks against Chang in those two sets.

"In the second and third sets he was able to dictate the points and I was having to play on the defensive," Chang said.

The rain, which was not hard enough to stop play, did not seem to greatly affect either player.

In Sydney, Wally Masur defeated Martin Jaite, 3-6, 6-7 (4-7), 6-4, 6-0, 6-2, in a three-hour struggle, giving Australia its 2-0 lead. Pat Cash swept past Alberto Mancini, 6-1, 6-1, 6-2, in the opening singles match on the grass court at White City.

Masur was given a pep talk from his teammates during the break after the third set.

"The guys told Wally he had to get his feet moving," said Australian captain Neale Fraser. "He came out dancing. It was a fantastic effort."

In a world group qualifying match for the 1991 Davis Cup, Henri Leconte and Guy Forget gave France a 2-0 lead over Britain at London. Leconte beat Nick Brown, 6-3, 7-6 (7-5), 6-2, and Forget downed Jeremy Bates, 2-6, 7-6 (7-5), 6-4, 6-1.

Britain must win in doubles today to stay alive in the best-of-five competition.