Hingis, the top seed, plays unseeded Anke Huber of Germany today and the third-seeded Williams meets No. 12 Barbara Schett of Austria tonight in the quarterfinals.

Four fourth-round men's matches take place today as fifth seed Gustavo Kuerten of Brazil faces Magnus Norman of Sweden, No. 14 Tommy Haas of Germany meets Cedric Pioline of France, and Jiri Novak squares off against countryman Slava Dosedel. Seventh seed Todd Martin of the United States battles No. 9 Greg Rusedski of Britain tonight.

The 1997 champion, Hingis managed a hard-fought 6-4, 7-5 win over 10th seed and 1994 champion Arantxa Sanchez-Vicario of Spain on Sunday. The 18-year-old from Switzerland owns a 15-1 record on hardcourts this summer, winning two titles. Her only loss was to Serena Williams in the semifinals at Manhattan Beach.

Hingis has won eight of nine meets with Huber, who is looking to oust her third straight seeded player. The German knocked off No. 8 Jana Novotna of the Czech Republic in the third round and 15th seed Amelie Mauresmo of France, 6-4, 6-4, in Sunday's fourth round.

Despite her losing record against the top seed, Huber has won more sets (10) off Hingis than all but three other players in this event: Lindsay Davenport, Novotna and Mary Pierce.

The 19-year-old Williams, who lost the Open final to Hingis in her debut two years ago and is seeded third this year, came back to defeat fellow American Mary Joe Fernandez, 2-6, 6-1, 6-0, on Sunday.

Williams, a winner over Schett in the only career meeting last year at Wimbledon, is looking to reach the semifinal of a Grand Slam for the first time since reaching the final four here a year ago.

Besides Hingis, Schett is the only other quarterfinalist to have dropped a set. She has lost just nine games in reaching her first career Grand Slam quarterfinal, winning three of four matches with the loss of just one game.

Kuerten is trying to reach his third straight Grand Slam quarterfinal. The Brazilian, three days short of his 23rd birthday, was the favorite going into the French Open but lost to Andrei Medvedev in the quarterfinals. He fell in the same round at Wimbledon to Andre Agassi.

Norman has never reached a Grand Slam quarterfinal but is tied with Pete Sampras for the tour lead in singles titles with four.

Martin brings a 5-1 record against Rusedski into tonight's battle. Their last encounter came during the United States' first-round tie against Britain in the Davis Cup, which Martin won in three straight sets.

Martin's season began with a 10-match winning streak that was stopped by Yevgeny Kafelnikov in the quarterfinals of the Australian Open. Martin has reached at least the quarterfinals in nine of 11 tournaments this season.

Rusedski has not won a title this season but came into this event having reached the final of the U.S. Pro Championships in Boston. He is trying to reach the quarterfinals at a Grand Slam for the first time since his runner-up finish here in 1997.

On Monday, second seed Agassi, Kafelnikov -- the second and third seeds, repectively, No. 12 Richard Krajicek, and unseeded Nicolas Escude reached the quarterfinals.

Second seed and defending champion Lindsay Davenport of the United States, fourth seed and two-time winner Monica Seles of the United States, No. 5 Mary Pierce of France, and American Serena Williams -- the seventh seed -- reached the final eight on the women's side.