Eighteen-year-old Californians Michael Chang and Pete Sampras battled for three hours under a scorching midday sun yesterday before Chang prevailed for a 3-6, 7-6 (7-5), 7-5 victory in the semifinals of the Canadian Open in Toronto.

Chang will face fourth-seeded Jay Berger, who outlasted unseeded Jakob Hlasek of Switzerland in the other semifinal, 3-6, 6-2, 6-2.

The fifth-seeded Sampras, formerly of Potomac, Md., said he blew the match in the last two sets.

"I should have won," said Sampras, who made 35 unforced errors to Chang's 17, the most critical in the third set.

"In the second set I just decided to give it my all," Chang said. "I was fortunate to win the tiebreaker -- I shouldn't have won it because of that one point."

In the tiebreaker, Chang took a 2-1 lead on Sampras's second serve with a shot that drove the crowd into wild applause. Sampras teed up an overhead smash, but Chang returned a winner.

Federation Cup: In Norcross, Ga., the top-seeded United States swept past Austria into the final to face the Soviet Union, which advanced after second-seeded Arantxa Sanchez Vicario, Spain's top player, was forced to retire with an ankle injury.

Fourteen-year-old Jennifer Capriati beat Barbara Paulus, 6-3, 6-4, and Zina Garrison defeated Judith Wiesner by an identical score to give the United States an unbeatable 2-0 lead over third-seeded Austria with the doubles match still to play.

Spain stood even with the fourth-seeded Soviet Union at one match apiece when Sanchez Vicario, Spain's top player with a No. 6 world ranking, had to retire trailing the Soviets' No. 1 player, Natalia Zvereva, 4-6, 0-2.