David Wheaton used a powerful serve and an aggressive game to upset Ivan Lendl 6-2, 7-6 (7-4) Friday to reach the semifinals of the $6 million Grand Slam Cup tennis tournament.

Wheaton, a 21-year-old two-year pro ranked 27th in the world, dominated from the first point to overpower Lendl, the world's third-ranked player and the top seed remaining in the tournament.His victory in one 1, 27 minutes made the semifinals of the richest tournament in tennis history an all-American affair.

Earlier, Brad Gilbert outlasted Aaron Krickstein in an error-filled match to win 6-7 (5-7), 6-4, 6-3.

Gilbert will play Wheaton in the semifinals on Saturday, while Pete Sampras will face Michael Chang.

"This is the biggest win of my career," Wheaton said. "I had a simple strategy and that was to hit as deep as I could and to try to keep him under pressure."

Wheaton broke Lendl in the opening game to set the tone of the match.

"I felt I had my range from the first point," he said.

Wheaton scored another break for a 4-1 lead, dropped his serve in the next game, but broke again to lead 5-2. Wheaton served out the set at love.

There were no breaks in the second set, but Wheaton was down 15-40 in the fourth game.

"He hit an ace with his second serve, then an unreturnable serve, then another ace. He served himself out of trouble," Lendl said.

Lendl himself fought off two break points in the ninth game.

Wheaton, seeded eighth, raced to a 3-0 lead in the tiebreak and had two match points.

Lendl saved the first with a brilliant return to the corner, but his next return went long.

"The court is fast and favors his game," Lendl said. "He took full advantage of it.

"I knew he can hit powerfully, but I was surprised how consistent he was. He deserves to be in the semifinal."

Lendl had 15 aces, Wheaton 11.

By getting to the semifinals, Wheaton made sure of winning at least $450,000, nearly doubling his career earnings of $481,712.

He said he was thinking "a bit" about the $2 million prize awaiting the winner.

"I don't know yet what I am going to do with the money, but my brother John will get more than a pair of socks for Christmas," he said.

Wheaton this year won his first tournament, at Charleston, and reached the quarterfinals at the U.S. and Australian Opens, and the round of 16 at Wimbledon.

Gilbert was also happy about the money.

"This is about three times more money than I ever made in a week and I feel great about it," said Gilbert, who only came to the tournament as a replacement for injured Andre Agassi. "And I can still make more."

Gilbert, ranked 10th in the world, was the only player able to hold serve in the third set, with both players repeatedly breaking each other.

"It was a typical match between us, there are always a lot of breaks," said Gilbert, now 4-4 against Krickstein in his career.

Krickstein dropped his serve in his last five service games.

The match between the two Americans was marked by sloppy play by both.