Andre Agassi kept his impressive run going while keeping Pete Sampras from staying No. 1.

The eighth-seeded Agassi beat the top-seeded Sampras 6-7 (7-5), 6-1, 6-2 Friday night in the quarterfinals of the $2.45 million du Maurier tennis tournament.Agassi, a three-time champion in this event, has won four tournaments this season, including both he has entered the last two weeks, improving his ranking more than 100 spots to No. 11.

His latest win will prevent Sampras from staying on top of the ATP world rankings. Sampras needed to win this event for the first time to maintain his No. 1 ranking. That spot will now be taken by Chile's Marcelo Rios, who briefly held the No. 1 spot earlier this year when Sampras was struggling to find his game.

Sampras won the first set in just over an hour, but the Wimbledon champion was nowhere to be found after that as Agassi won the second set in 28 minutes and the third in 30 minutes.

"Once his legs start going he becomes a different player," Agassi said of Sampras.

After the first set it was clear Agassi was the fresher of the two. Both had to play two matches Friday because of a rain delay Thursday, but Agassi was the one with eagerness in his game. Sampras seemed more pre-occupied will line judges and close shaves.

"As the match went on I felt myself getting slower and slower," Sampras said. "He didn't have to do much in the second and the third sets."

In today's semifinals, Agassi will face No. 6 Richard Krajicek of the Netherlands, while third-seeded Patrick Rafter of Australia will meet No. 7 Tim Henman of England.

In the other quarterfinals, Rafter defeated No. 5 Jonas Bjorkman of Sweden 6-3, 6-2; Henman beat unseeded Daniel Vacek of the Czech Republic 6-3, 5-7, 6-2; and Krajicek beat No. 4 Yevgeny Kafelnikov of Russia 6-4, 6-4.

Agassi advanced to the quarterfinals with a 2-6, 7-5, 6-3 victory over No. 10 Goran Ivanisevic of Croatia, who lost the match when he double-faulted on match point.

Sampras, after a three-hour rain delay, appeared sluggish, tired and frustrated in a 7-6 (7-5), 6-2 victory over Tommy Haas of Germany.

Against Agassi, Sampras' serve won him the first set - when he had 11 of his 22 aces. With declining speed and much less accuracy, Sampras uncharacteristically double-faulted 12 times in the match, nine times more than Agassi. Sampras capped it by making 50 unforced errors.

TOSHIBA CLASSIC: Venus Williams withdrew due to a leg injury Friday from her quarterfinal-round match against France's Mary Pierce in the $450,000 Toshiba Tennis Classic.

Williams, the No. 3 seed, retired after falling behind 4-0 in the third set with what she said was patella tendinitis in her left knee.

Williams, 18, won the first set 6-2, Pierce the second 7-6 (7-3).

Williams said she wasn't worried the injury might keep her out of the U.S. Open at the end of the month.

"I don't feel that it's going to be something that's going to hold me back," she said. "It's something that's temporary right now."

Second-seeded Lindsay Davenport moved into the semifinals with a 6-4, 6-3 victory over eighth-seeded Nathalie Tauziat of France in the featured night match.

Davenport rallied from 3-0 deficits in each set to beat Tauziat, runner-up this year at Wimbledon.

Williams, ranked fifth in the world, said the knee flared up at 4-4 in the second set.

After holding serve to go up 6-5 in the set, Williams limped noticably to her courtside chair and requested an injury timeout. After receiving treatment from a WTA trainer, Williams returned with a bandage on her left knee.

The injury clearly hampered Williams for the remainder of the match before she retired.

"I thought maybe I could still win the match," she said. "I found that I was living in a false reality. When I realized that, I quit."

Fourth-seeded Monica Seles continued to feel the effects of a back injury that has plagued her since last month. Seles, who defeated Ai Sugiyama of Japan 6-4, 6-3 in another quarterfinal match, said her back continues to "spasm after every match."

Seles cast doubt about whether she would be able to finish the tournament and said she could pull out of next week's Acura Classic at Los Angeles.

Pierce, who hurt her wrist late in first set, said she "came close to quitting myself because I was having trouble gripping" the racket.

Following her injury, Williams did not last long.

Pierce immediately held serve to tie the match 6-6 and force a tiebreaker, which she won after bolting to a 6-1 lead.

After Pierce won the first game of the third set, Williams labored with her serves. Williams, among the tour's fastest servers, had a 67 mph serve as Pierce broke service in the second game.

When Pierce broke again in the fourth game, Williams walked over to chair umpire Anne Lassere Ullrich and told her that she couldn't continue.

Williams said she had two leg injuries Sunday during a match at Stanford, Calif., against Davenport. Williams didn't specify the injuries but said one was related to Friday's injury.