WIMBLEDON, England (AP) -- Venus and Serena Williams are one match away from a sibling showdown in the Wimbledon semifinals, and Martina Hingis will try to keep it from happening.

All three women won in straight sets Monday. In Tuesday's quarterfinals, the top-seeded Hingis will play No. 5 Venus Williams, and No. 8 Serena Williams will face unseeded American Lisa Raymond.

The winners meet Thursday, with the Williams sisters hoping to play each other for only the second time in a Grand Slam tournament.

``We'd like to have that opportunity,'' Venus said. ``At least one Williams would be in the final.''

``Now the tournament begins,'' Hingis said. ``They played very well so far, and so did I.''

The warmest day of the tournament produced few surprises, except for a naked male fan who interrupted a women's doubles match involving Anna Kournikova. The man ran onto court 14, stripped, waved his arms, danced and tumbled over the net before being taken away by guards.

``I wasn't paying attention to it,'' Kournikova said. ``I was just trying to think about the match.''

Second-seeded defending champion Lindsay Davenport beat Jennifer Capriati 6-3, 6-3 in the final women's match of the day. Davenport's opponent in the quarterfinals will be No. 6 Monica Seles, who beat No. 9 Arantxa Sanchez-Vicario 6-3, 6-4.

After the worst Grand Slam showing by American players in the open era at the French Open, five U.S. women are among the eight quarterfinalists.

``American tennis, at least on the female side, is looking up,'' Serena Williams said. ``I don't know what it is. Maybe it's McDonald's.''

In men's play, six-time champion Pete Sampras showed no ill effects from the sore shin that bothered him last week. He notched his 25th consecutive victory at the All England Club, beating Jonas Bjorkman 6-3, 6-2, 7-5.

Sampras said his shin was better but still sore.

``For the first time, the pressure's on my opponents a little, because they know I'm a little injured,'' he said. ``And they're not liking it.''

Second-seeded Andre Agassi beat qualifier David Prinosil 6-4, 6-3, 6-3. Agassi's opponent Wednesday will be No. 10 Mark Philippoussis, who won his second consecutive five-setter, beating No. 8 Tim Henman 6-1, 5-7, 6-7 (9), 6-3, 6-4.

Sampras' next opponent will be American Jan-Michael Gambill, a Grand Slam quarterfinalist for the first time. Gambill beat No. 9 Thomas Enqvist 7-6 (5), 3-6, 6-3, 6-4, leaving Sampras as the only seeded player in his half of the draw.

Darkhorses Vladimir Voltchkov of Belarus and Alexander Popp of Germany advanced. Voltchkov, a qualifier ranked No. 237, beat Wayne Ferreira 6-3, 6-4, 7-6 (0). In a matchup of two 6-foot-7 players, Popp defeated Marc Rosset 6-1, 6-4, 3-6, 4-6, 6-1.

Popp will next play No. 12 Patrick Rafter, who beat Thomas Johansson 6-3, 6-4, 6-7 (4), 6-1.

The only Williams-Williams matchup in a major came at the 1998 Australian Open, with Venus beating her younger sister in the second round.

``I'm ready to play Venus or Hingis or whoever,'' Serena Williams said. ``I'm playing very well. I'll just have to take it as it comes.''

Hingis prevented a showdown between the sisters at last year's U.S. Open by beating Venus in the semifinals. Serena then defeated Hingis in the final.

Venus said she's not afraid of Hingis, who is ranked No. 1.

``So what?'' Williams said. ``I've played Martina thousands of times.''

They've actually played 14 times, with Hingis winning nine. Hingis is 3-0 against Venus in Grand Slam tournaments. They've never met on grass.

Venus was erratic but overpowering in beating Sabine Appelmans 6-4, 6-4 to reach the quarterfinals for the third year in a row. She then watched from the stands as her sister completed a 6-1, 6-1 victory over Tamarine Tanasugarn.

Hingis beat No. 11 Anke Huber 6-1, 6-2.

Raymond advanced to her first Grand Slam quarterfinal by beating Olga Barabanschikova 6-4, 6-2. Two other unseeded Americans, Lilia Osterloh and Kristina Brandi, were eliminated.

Osterloh lost to Magui Serna 7-6 (1), 6-3. Brandi was beaten 6-1, 6-3 by Jelena Dokic, 17, who reached the quarterfinals for the second year in a row.

On the men's side, Byron Black reached his first Grand Slam quarterfinal since 1995 by beating 35-year-old Gianluca Pozzi 4-6, 7-6 (5), 6-2, 6-4.

Venus Williams had trouble finishing off Appelmans, who erased three match points serving at 1-5, 0-40 in the second set. Williams then double-faulted twice to lose her serve for the only time before closing out the match two games later.

``I just made some errors,'' she said. ``There were a lot of easy shots I missed. I don't usually do that.''

Her father, Richard, attending Wimbledon for the first time, watched with photographers in the first row behind the baseline on court two. He was back in the stands for Serena's match.

The younger Williams has lost only 11 games in four rounds.

``I don't want to come all this way to get only so far,'' the U.S. Open champion said. ``I'm ready to go all the way now.''