Hingis, the top seed and a former U.S. Open champion, will oppose 10th seed Arantxa Sanchez-Vicario of Spain, also a former Open champion. Williams, who made the Open final in her debut two years ago and is seeded third this year, goes against fellow American Mary Joe Fernandez, who is unseeded.

There are two other fourth round matches involving seeded women Sunday. Number 12 Barbara Schett of Austria will go against Elena Likhovtseva of Russia and 15th seed Amelie Mauresmo of France faces Anke Huber of Germany.

Among the seeded men in third round action, fifth seed Gustavo Kuerten of Brazil opposes Goran Ivanisevic of Croatia, number seven Todd Martin of the United States takes on Magnus Larsson of Sweden, ninth seed Greg Rusedski of Britain, a losing finalist two years ago, plays American Chris Woodruff and 14th seed Tommy Haas of Germany tangles with Hicham Arazi of Morocco in a night match.

There are four third round matches scheduled featuring unseeded men. One-time Open finalist Cedric Pioline of France plays Peter Wessels of the Netherlands, Jiri Novak of the Czech Republic goes against Fabrice Santoro of France, Magnus Norman of Sweden plays Richard Fromberg of Australia and Slava Dosedel of the Czech Republic faces Fredrik Jonsson of Sweden.

Hingis, who won the Open in 1997 and was the losing finalist to American Lindsay Davenport last year, has dominated Sanchez-Vicario, winning 11 consecutive matches after losing their first encounter. In their last meeting, Hingis routed Sanchez-Vicario, 6-1, 6-1, in the quarterfinals at Toronto.

Sanchez-Vicario, who won the Open in 1994, once was ranked No. 1 in the world but has struggled with her game this year. She won only two of her first six matches this year and is battling to remain in the top 10.

Williams has won five tournaments this year to reach a career-high No. 3 three ranking. She entered the Open coming off a straight sets victory over Davenport in the finals at New Haven, Connecticut. This will be her first match against Fernandez, who is playing in her 13th U.S. Open.

Fernandez once was ranked fourth in the world and made the finals of four Grand Slam events, but she has been plagued by a variety of injuries this season. She upset Serena Williams in the third round of the French Open this year but has seen her ranking fall to 38th in the world.

Mauresmo, the losing finalist to Hingis at the Australian Open, also is trying to come back from an injury and like Hingis and Williams, will be going against a former top 10 player in Huber. Mauresmo earlier this year became the first woman outside the top 10 to beat two number one ranked players in the same year. She defeated Davenport at the Australian Open and downed Hingis at the Paris Indoors. Mauresmo suffered an ankle injury in the French Open and has played only two tournaments leading up to the U.S. Open.

Huber, once ranked fourth in the world, has struggled this year, compiling only a 23-17 record and seeing her ranking dip to 27th. She routed eighth seed Jana Novotna of the Czech Republic, 6-2, 6-2, to reach the fourth round.

Kuerten, a former French Open champion, will be trying to advance to the fourth round of his fourth consecutive Grand Slam event. He reached the quarterfinals of the French Open and Wimbledon before losing. Ivanisevic has beaten two qualifiers to reach the third round and he has lost five of his last six matches to seeded players at Grand Slam events. Overall, Ivanisevic is 10-16 against seeded players in Grand Slam play.

Martin is 2-4 lifetime against Larsson but has won their last two matches. Martin is seeking to reach the fourth round of the U.S. Open for the first time since 1995. Earlier this year, he made the quarterfinals at the Australian Open and Wimbledon.

Rusedski, who lost in the finals to Australia's Patrick Rafter two years, ago, and Woodruff have never played each other. Woodruff is attempting to reach the fourth round of a Grand Slam event for the first time in his career.

In Saturday's major action, Americans Andre Agassi and Jennifer Capriati continued their comeback heroics with victories. Agassi, who resurrected his career this year by winning the French Open and making the Wimbledon finals, took out fellow American Justin Gimelstob in four sets. Capriati, the former teen prodigy who says she has been inspired by Agassi's resurgence, ousted 11th seed Nathalie Tauziat of France in three sets.