However, defending champion and fifth seed Amanda Coetzer of South Africa was ousted by No. 16 Henrieta Nagyova of Slovakia, 6-2, 6-3. Last year, Coetzer won the biggest title of her career here and became the lowest seed (No. 4) to win the event.

In other matches of note, second seed and 1997 runner-up Monica Seles of the United States will take on No. 14 Elena Likhovtseva of Russia tonight, and third-seeded Czech Jana Novotna leads No. 13 Silvia Farina of Italy, 5-7, 7-5, 4-3 in a match currently suspended by rain.

Seeking her first title in two months, Hingis fell behind the 10th-seeded Spaniard, 2-4, in the first set before winning 11 of the next 13 games.

"I played terrible in the beginning," Hingis said. "I was not really into it and I got myself down. But I kind of picked up my game, especially in the second set. I started making more winners. I was making some shots I would miss before and it was a big change."

Hingis improved to 7-2 lifetime against Martinez, earning her first win on clay over the Spaniard in three tries.

Making her first appearance at Hilton Head since earning the title here in 1997, the 18-year-old Hingis has not claimed a title since defeating Coetzer in the Pan Pacific Open in Japan on February 7. She also won her third straight Australian Open singles title in January.

Hingis will take on No. 11 Natasha Zvereva of Belarus in Friday's quarterfinals. Zvereva dispatched Nathalie Dechy of France, 6-3, 7-6 (7-4).

In other third-round play, sixth seed Patty Schnyder of Switzerland downed Iva Majoli of Croatia, 7-6 (7-2), 6-3; seventh-seeded Russian teenager Anna Kournikova got past No. 12 Barbara Schett of Austria, 7-6 (8-6), 6-4; and Germany's Andrea Glass defeated Spain's Gala Leon Garcia, 6-4, 6-3, in a match involving unseeded players.

Kournikova and Glass will square off in the quarterfinals.

First prize is $150,000.