However, third seed and four-time champion Steffi Graf of Germany aggravated a left hamstring strain and retired from tonight's second-round match with American Amy Frazier while trailing 4-6, 7-5, 2-1.

Hingis, the second seed and 1997 champion, fell behind 2-4 in the opening set before breaking back in the next game. After breaking Rubin to take a 5-4 lead, Hingis was broken as she served for the set. But the Swiss teenager broke Rubin in the next game for a 6-5 lead and served out the set.

With the momentum on her side, Hingis immediately broke Rubin in the opening game of the second set and never lost her serve again, securing a quarterfinal berth with her fifth break.

Hingis' surprising 6-2, 6-0 loss to Australian teenager Jelena Dokic in the first round at Wimbledon was her worst Grand Slam result in five years and came on the heels of her setback to Graf in the final of the French Open.

Hingis was booed off the court in Paris after the 18-year-old repeatedly challenged calls and even walked over to Graf's side of the court.

After her loss in London, Hingis took several weeks away from the game to sort out her personal and professional life. She took a break from her coach and mother, Melanie Molitor, who is back with her this week.

Hingis has won four titles this season, including the Australian Open, and improved to 44-7 overall with today's win.

Rubin could not duplicate her performance of five months ago, whe she defeated Hingis -- ranked No. 1 at the time -- in the quarterfinals at the Evert Cup in Indian Wells, California.

Graf also was competing in her first event since her loss to Davenport in London in what turned out to be the German's last appearance at the All-England Club. She played that match with the same leg injury that plagued her tonight.

Afterwards, Graf said she did not know how long this latest ailment would keep her sidelined. She is next scheduled to play at the Canadian Open in Toronto in two weeks.

The German star, who has hinted at retiring at the end of the season, had won 13 of her previous 14 matches and fell to 16-6 on hardcourts this year. She won this tournament in 1989-1990 and 1993-94.

In first-round action, sixth seed Arantxa Sanchez-Vicario of Spain got past Russia's Elena Likhovtseva, 6-2, 1-6, 6-4, and seventh seed Amanda Coetzer of South Africa rallied past American Lisa Raymond, 6-7 (1-7), 6-1, 6-1.

German qualifier Anke Huber posted the lone upset of the day session as she upended eighth seed Nathalie Tauziat of France, 6-3, 6-1.

Also, Russian teenager Anna Kournikova defeated American qualifier Meilen Tu, 6-2, 7-6 (7-3); Natasha Zvereva of Belarus raced past Fabiola Zuluaga of Colombia, 6-2, 6-1; and Dominique Van Roost of Belgium beat Canada's Maureen Drake, 6-3, 7-5.

Tonight, Sandrine Testud downed Australian Open runner-up Amelie Mauresmo, 6-4, 6-0, in an all-French affair.

Davenport, the top seed, is one-third of the way toward duplicating her California sweep of a year ago. She is 16-1 in her last 17 matches in her home state, dating to last year, when she swept all three summer hardcourt tournaments in California.

The only loss for the 23-year-old Newport Beach resident in that span was to American Serena Williams at Indian Wells in March.

Davenport successfully defended her title at the Bank of the West Classic in Stanford on Sunday, defeating Serena's older sister Venus, 7-6 (7-1), 6-2. The reigning Wimbledon champion is 33-5 this season, including 18-3 on hard courts and will try to win her second straight U.S. Open later this summer.

Seeded fourth, Venus Williams tries to rebound from her loss in Sunday's final as she seeks her fifth title of the year. She is 36-7 in 1999 and has won 13 of 14 matches on hardcourts. Her loss to Davenport was just her fourth in 24 matches on hard surfaces this season.

Davenport, Hingis, Graf and Williams all received first-round byes.

First prize is $80,000.