Hingis, the top seed, dumped Russia's Elena Likhovtseva, 6-4, 6-1. Graf, seeded third, improved to an amazing 73-5 lifetime at this event by defeating Cara Black of Zimmabwe, 7-6 (7-5), 6-2.

Sanchez-Vicario, the fourth seed and 1995 champion, pulled out a dramatic 6-1, 0-6, 7-5 victory over defending champion and 14th-seeded countrywoman Conchita Martinez.

After losing the first set, Martinez won 10 straight games. She served for the match at 5-4 in the third set but was broken and never won another game.

"It was an amazing match," Sanchez-Vicario said. "Conchita played really well in the second set and at the start of the third, but I just kept fighting and never gave up."

Hingis, 10-1 on clay this season, will meet No. 16 Barbara Schett of Austria in Friday's quarterfinals. Schett outlasted sixth seed Nathalie Tauziat of France, 6-1, 4-6, 7-6 (7-5), but will have an even more difficult task against Hingis after dropping all six previous meetings with the world's top-ranked player.

Seventh-seeded teenager Serena Williams, seeking her third title of the year, won two matches against fellow Americans to earn a quarterfinal meeting with Sanchez-Vicario on Friday. After completing a 7-6 (7-3), 6-3 second-round win over Jennifer Capriati from Wednesday, Williams downed Lisa Raymond, 6-1, 7-6 (7-1).

In other third-round action, eighth seed Patty Schnyder of Switzerland rallied past Anna Smashnova of Israel, 2-6, 7-6 (7-3), 6-1, and will meet unseeded Ruxandra Dragomir of Romania on Friday. One day after stunning second seed Jana Novotna, Dragomir knocked off No. 12 Amelie Mauresmo of France, 6-2, 7-5.

Unseeded Julie Halard-Decugis of France will face Graf on Friday after crushing Pavlina Stoyanova of Bulgaria, 6-1, 6-0. Halard-Decugis is 0-9 lifetime against Graf, including 0-4 on clay.

First prize is $150,000.