Top seed Anna Chakvetadze has ousted Casey Dellacqua from the New Haven ATP tournament in straight sets.
Russian Chakvetadze won 6-4 6-4 against the Australian women's No.1 in the second round, but two other seeds have been eliminated.
Fifth seed Patty Schnyder was edged by Amelie Mauresmo 6-4 3-6, 7-6 (8-6), while No.6 Flavia Pennetta was defeated by Sorana Cirstea of Romania 3-6 6-4 6-3.
Mauresmo improved to 13-6 against Switzerland's Schynder, and maintained her record of never losing before the quarter-finals at New Haven. She reached the final once, in 2005.
Cirstea will play Chakvetadze in the quarter-finals.
Caroline Wozniacki of Denmark, a 6-3 6-3 winner over Monica Niculescu of Romania, next meets third-seeded Marion Bartoli.
In the men's draw, fourth seed Igor Andreev defeated Victor Hanescu of Romania 6-4 7-5 to reach the New Haven quarter-finals for a third time.
Andreev, twice a finalist this year, will bid for a maiden semi-finals berth in New Haven against sixth-seeded Marin Cilic, who overcame Jurgen Melzer of Austria 5-7 6-4 7-5.
No.7 seed Andreas Seppi defeated fellow Italian Fabio Fognini 6-4 6-2 in his third-round match, and American Jesse Levine advanced to his first quarter-finals on the main tour when Belgian opponent Steve Darcis retired with a back injury during the first set.
