SYDNEY, Australia (AP) -- Top-ranked Martina Hingis, despite an injured foot, won in straight sets over No. 5 seed Serena Williams on Thursday to advance to the semifinals at the Adidas International.

Hingis said a blister on her right foot prevented her from teaming with Monica Seles for a doubles semifinal against Lisa Raymond and Rachel Stubbs, but she expected to be ready Friday to play Conchita Martinez in singles.

Martinez, the No. 4 seed, advanced with a 6-4, 6-0 win over Corina Morariu of the United States.

Defending titlist Amelie Mauresmo overcame back pains to oust Seles 6-4, 7-6 (5) and move into a semifinal -- a replay of last year's final -- against second-seeded Lindsay Davenport.

Davenport swept Raymond 7-5, 6-4 in an all-American quarterfinal.

Hingis, who won three successive Australian Opens before losing last year to Davenport, said the Adidas International has not been successful warmup for her since she won it in 1997.

But her 6-4, 7-5 win against the big-serving Williams is a confidence booster, she said.

The 20-year-old Swiss star broke Williams in the opening game and maintained that advantage for the balance of the first set. Hingis rallied from 4-1 down to clinch the second set.

After completing her second win in three days against Serena -- she and Seles combined to end Venus and Serena Williams' 22-match winning streak in doubles -- Hingis said she wasn't afraid of the powerful American sisters.

``The more you play them, the less problems you will have,'' Hingis said. ''... other girls are already intimidated, but I'm the No. 1 player, so I just have to defend my position. I shouldn't be scared.''

Williams said she was ``rusty,'' but vowed to improve at next week's season-opening Grand Slam.

``I'm getting my rhythm back. I felt it a little in this game,'' she said. ``Next week, I should do a lot better because I have it, I'm just working on getting it out there.''

Mauresmo was having treatment late Thursday on the back injury. She said she hoped it was nothing more than a muscle strain.

Trailing 3-2 in the second, the Frenchwoman called for a medical timeout so that the trainer could treat the injury, a problem that plagued her last season and sidelined her for four months.

Then, leading 5-3 in the tiebreaker, Mauresmo thought she won a point that would give her three match points.

But Australian umpire Leanne White called for the point to be played again. Mauresmo lost the replay and the next point, tying the score 5-5. But she won the last two points to clinch the tiebreaker.

``I lost against her twice before, so I really wanted to make it this time,'' she said. ``It wasn't an easy match, but I handled it very well.''

In men's quarterfinals, top-seeded Magnus Norman overcame George Bastl of Switzerland 6-4, 3-6, 6-3 to set up an all-Swedish semifinal against Jonas Bjorkman, who beat German Rainer Schuttler 6-3, 6-4

Defending titlist Lleyton Hewitt fought back from 1-3 down in the first set to overcome Fabrice Santoro of France 6-4, 6-1.

Hewitt, the No. 2 seed, faces a semifinal against No. 6 Sebastien Grosjean of France, who swept unseeded Swiss Roger Federer 7-5, 6-4.