MANHATTAN BEACH, Calif. (AP) -- Martina Hingis and Lindsay Davenport, each bothered by nagging injuries as they tune up for the U.S. Open, won quarterfinal matches Friday in the estyle.com Classic.

No. 3 seed Kim Clijsters of Belgium wasn't so lucky. The 18-year-old lost 7-6 (3), 6-3 to fifth-seeded Nathalie Tauziat of France.

Two-time defending champion Serena Williams played sixth-seeded Monica Seles in a later match.

Hingis, the top seed, defeated No. 12 Amy Frazier 6-2, 6-3 in 69 minutes to set up a semifinal with either Williams or Seles.

``I didn't play the best game today, but it was good enough against Amy,'' Hingis said. ``I'll have to step it up tomorrow if I want to have a chance.''

Hingis has been bothered by a recurring stress reaction to her left foot since last week's Acura Classic in Carlsbad. She withdrew from next week's tournament in Toronto, and once she's done in California she plans to rest until the U.S. Open begins Aug. 27.

``Even today I was very cautious with my foot,'' she said. ``It's not getting worse, it's just like the same pain. Something is going on there. Hopefully it's going to be fine until the U.S. Open, that's what I'm most worried about.''

Davenport struggled for the second time in three matches before beating seventh-seed Elena Dementieva of Russia 5-7, 6-4, 6-2. She will play Tauziat in Saturday's other semifinal.

``It was one of those days where I got through and maybe I shouldn't have,'' she said. ``I felt like I was missing balls for no reason, not going for winners. I was really fed up with how I was giving her the match.''

Davenport also withdrew from Toronto, citing left wrist tendinitis aggravated in a semifinal loss to Venus Williams last week.

``It's getting more tender as the week goes on,'' she said. ``It's been my Achilles' heel since 1996 as far as injuries go. It's not anything I need a MRI for.''

Davenport also rolled her right ankle in the final game against Dementieva, but was pronounced fit by a WTA Tour trainer.

``I was so spastic. I kind of tripped,'' she said, laughing.

Not funny is Davenport's continued erratic play, including hitting groundstrokes well beyond the lines. After being broken at 1-1 in the third set, she dropped and kicked her racket in frustration.

``I got up a break and then got broken. That's pretty bad,'' she said. ``I feel like mentally and physically I'm going down and I cannot afford that going into the U.S. Open.''

Clijsters, who beat Davenport for her first title this year two weeks ago in Stanford, had nine double faults against the 33-year-old Tauziat.

``I played one of my best matches. She didn't serve well. Maybe she was afraid of my return,'' said Tauziat, who plans to retire at year's end.

``I still enjoy playing, what bothers me is not being able to enjoy the other parts in my life. I want to enjoy something else. I gave 15 years to tennis, that's enough.''