MUNICH, DEC. 14 -- David Wheaton, a two-year pro from Minnesota ranked 27th, upset Ivan Lendl, 6-2, 7-6 (7-4), today to reach the semifinals of the $6 million Grand Slam Cup, leaving only Americans in the tournament.

Wheaton used a powerful serve and an aggressive game to upset Lendl, ranked third, in 1 hour 27 minutes. Earlier, Brad Gilbert outlasted Aaron Krickstein in an error-filled match, 6-7 (5-7), 6-4, 6-3.

Gilbert will play Wheaton on Saturday and 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."

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

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

There were no breaks in the second set. Wheaton took a 3-0 lead in the tiebreaker and converted his second match point when Lendl's return went long.

By winning the match, Wheaton made sure of earning at least a losing semifinalist's share of $450,000, nearly doubling his career winnings of $481,712.

He said he has begun to think "a bit" about the $2 million prize awaiting the winner of the richest tennis tournament in history.

"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 won his first tournament at Charleston this year and reached the quarterfinals at the U.S. and Australian opens and the round of 16 at Wimbledon. Players qualified for this tournament based on their performances in the four Grand Slam events.

In the first match, only 10th-ranked Gilbert held serve in the third set. Krickstein lost his last five service games.

The match was punctuated by sloppy play, Gilbert having 41 unforced errors and Krickstein committing 36.

After Gilbert won the second set to even the match, neither player held serve until the fifth game of the third set. That's when Gilbert served an ace to hold at love and take a 3-2 lead. He then broke 20th-ranked Krickstein for what proved to be an insurmountable 4-2 advantage.

Gilbert qualified for this event only after Andre Agassi pulled out because of an injury.

"This is about three times more money than I ever made in a week and I feel great about it," Gilbert said, "and I can still make more."