NEW YORK (AP) - It's been so one-sided, it's hard to call it a rivalry.

It will be the 12th meeting between Martina Hingis and Arantxa Sanchez-Vicario when they face each other in the fourth round of the U.S. Open. And after Sanchez-Vicario captured their first meeting, it's been all Hingis.

``You have to take her serious,'' the top-seeded Hingis said of the Spanish veteran. ``But I know I won the last matches quite easily, so that's why I kind of can't go out there and think, `Yeah, it's going to just happen.'''

Hingis clinched a spot in the fourth round of the year's final Grand Slam tournament by defeating qualifier Sandra Kloesel of Germany 6-2, 6-2. Sanchez-Vicario advanced with a 6-2, 6-2 drubbing of Patty Schnyder, a one-time Swiss Fed Cup teammate of Hingis.

``I have nothing to lose,'' Sanchez-Vicario said. ``She beat me the last many times we play.

``You know you have to take your opportunities, even if you don't have too many. That's what makes a difference.''

Other fourth-round matchups determined Friday will pit No. 15 Amelie Mauresmo against Anke Huber, No. 3 Venus Williams against Mary Joe Fernandez, and No. 12 Barbara Schett against Elena Likhovtseva.

Mauresmo defeated Tara Snyder 6-4, 6-3; Huber upset No. 8 Jana Novotna 6-3, 6-2; Fernandez surprised No. 13 Dominique Van Roost 7-5, 6-0; Schett stopped Virginia Ruano Pascual 6-1, 6-0, and Likhovtseva downed Irina Spirlea 6-1, 6-3.

In men's play Friday, five of the 16 matches went to five sets.

Jiri Novak of the Czech Republic defeated Russian Marat Safin 6-2, 5-7, 6-4, 3-6, 6-2; Frenchman Fabrice Santoro won when Jan-Michael Gambill of Colbert, Wash., retired because of leg cramps with the score tied 6-4, 6-2, 3-6, 6-7 (4-7), 4-4; Cedric Pioline of France edged German Lars Burgsmuller 7-6 (7-5), 1-6, 6-3, 3-6, 6-2; No. 14 Tommy Haas of Germany downed Argentina's Mariano Puerta 6-3, 6-2, 2-6, 6-7 (3-7), 6-1; and Goran Ivanisevic of Croatia ousted Italy's Cristiano Caratti 6-1, 4-6, 6-2, 2-6, 6-4.

Other winners on the men's side were No. 5 Gustavo Kuerten; No. 7 Todd Martin; No. 9 Greg Rusedski; Slava Dosedel of the Czech Republic; Sweden's Fredrik Jonsson; Chris Woodruff of Knoxville, Tenn.; Swede Magnus Larsson; Dutchman Peter Wessels; Hicham Arazi of Morocco; Australian Richard Fromberg, and Sweden's Magnus Larsson.

By the end of his match, Gambill was cramping so much he hit one serve underhanded. Finally he turned to the umpire, said, ``That's it. I cannot move. End of the match,'' and threw his racket toward his chair.

For Ivanisevic, it was either ace or double-fault. He ended with 15 aces and 18 doubles, including four doubles in the final game of the fourth set.

In that game, he had three double-faults, then hit a clean ace. However, it was called a fault before Caratti showed where the ball had landed inside the service box. Ivanisevic, given another chance, promptly double-faulted again.