Hingis capitalized on 49 unforced errors and took a 5-4 lead in the all-time series. She will face fourth seed Conchita Martinez of Spain in the semifinals.

"It was a good match," said Hingis, the world's top-ranked player. "It wasn't perfect and there are still a few things I need to improve on, but it was great for the confidence. Every win you have is a good one."

A semifinalist here in 1998, Williams committed back-to-back unforced errors that enabled Hingis to break in the pivotal 11th game of the second set. Hingis held serve to close out the match.

"I'm still a little rusty," Williams admitted. "It was only my third match since October, so I'm doing well, considering. I've got my attitude back, which is the important thing."

Also on Thursday, Hingis was selected as the top seed in next week's Australian Open.

Second seed Lindsay Davenport of the United States moved into the semifinals with a 7-5, 6-4 triumph over fellow American Lisa Raymond.

The 1999 champion and runner-up last year, Davenport will face France's Amelie Mauresmo on Friday after the defending champion surprised third seed Monica Seles, 6-4, 7-6 (7-5).

Mauresmo overcame a recurrence of her back injury to become only the second woman to defeat Seles in Australia. Seles' only other loss on this continent came against Hingis in the semifinals of the 1999 Australian Open.

"Hopefully, it is just muscle tightness, not the same injury that I had last year," Mauresmo said. "But I won't know for sure until I get some treatment."

Martinez earned her spot in the semifinals with a 6-4, 6-0 sweep of Corina Morariu of the United States.

On the men's side, top seed Magnus Norman of Sweden struggled to a 6-4, 3-6, 6-3 triumph over Swiss qualifier George Bastl.

Norman, who won five titles last season and reached the final of the French Open, has rebounded nicely from a first-round loss last week in India.

Defending champion Lleyton Hewitt of Australia takes on Fabrice Santoro for a spot in the semifinals. The second seed is coming off a 6-4, 6-1 victory over Andrew Ilie.

Sixth seed Sebastien Grosjean of France rolled to a 7-5, 6-4 victory over Swiss teenager Roger Federer. And Sweden's Jonas Bjorkman disposed of Germany's Rainer Schuttler, 6-3, 6-4.