No. 1 Pete Sampras of the United States and two-time defending champion Patrick Rafter were forced to withdraw from the tournament Tuesday with injuries, leaving the top half of the men's draw wide open.

But 15 of 16 women's seeds still remain, including Hingis. The 1997 champion plays Sarah Pitkowski of France today. Williams faces Anne-Gaelle Sidot of France tonight.

After back-to-back losses at the French Open and Wimbledon, Hingis has bounced back to win two tournaments during the summer hardcourt season and reclaim the No. 1 ranking. The teenager has won a WTA Tour-leading six events this season, including her third straight Australian Open title in January.

Hingis lost to the now-retired Steffi Graf in the French Open final and followed that defeat with a humiliating 6-2, 6-0 first-round loss to Jelena Dokic. She got off to a good start here on Monday with a 6-1, 7-5 victory over Kveta Hrdlickova of the Czech Republic.

Williams, regarded as one of the favorites to win her first Grand Slam singles title at the Open, crushed Tatiana Poutchek, a 20-year-old qualifier from Belarus, 6-1, 6-2, Monday.

A finalist in 1997 in her U.S. Open debut and a semifinalist last year, the 19-year-old Williams has looked impressive over the past month. She reached consecutive finals at California events in Stanford and San Diego and defeated Davenport to win last week's Pilot Pen in New Haven, Connecticut, her fifth title of 1999.

In other second-round matches involving seeded women, No. 8 Jana Novotna of the Czech Republic meets Slovenia's Tina Krizian; 10th seed and 1994 winner Arantxa Sanchez-Vicario of Spain battles Australian Nicole Pratt; 12th-seeded Barbara Schett of Austria takes on Sweden's Asa Carlsson; No. 13 Dominique Van Roost of Belgium squares off against Italy's Rita Grande; and No. 15 Amelie Mauresmo of France matches up against South African Mariaan De Swardt.

Only two men's second-round matches are on the schedule. No. 3 Yevgeny Kafelnikov of Russia takes on his occasional doubles partner Max Mirnyi of Belarus. The winner will face former semifinalist Jonas Bjorkman of Sweden or Denmark's Kenneth Carlsen in the third round. Bjorkman and Carlsen square off today.

Kafelnikov, who battled with the wind but got past Alberto Martin of Spain, 6-1, 3-6, 6-3, 6-4 on Monday, won his second career Grand Slam title in January at the Australian Open. He became the first Russian to be ranked No. 1 despite a seven-match losing streak in May.

However, the Russian has regained his form this summer by reaching the quarterfinals or better at five straight events, including runner-up finishes at the Super 9 du Maurier Open and the Legg Mason Classic.

A lucky loser who took the spot vacated by Sweden's Thomas Johansson, Mirnyi beat Tomas Zib of the Czech Republic on Monday in five sets. Although born in Minsk, Mirnyi trained at the Brooklyn Racquet Club as a teenager while briefly living in the predominantly Russian Brighton Beach section.

In first-round action, ninth seed Greg Rusedski of Britain plays Juan Carlos Ferrero of Spain; No. 14 Tommy Haas of Germany meets Sweden's Tomas Enqvist; No. 17 Felix Mantilla of Spain encounters Sweden's Magnus Norman. Mantilla took the place in the draw of Mark Philippoussis, the 16th seed who is still recovering from knee surgery.

Mikael Tillstrom of Sweden took Sampras' place and will square off against Russian teenager Marat Safin, who is fresh off claiming his first career ATP tournament in Boston.