Top-seeded Agnieszka Radwanska of Poland slipped past American Varvara Lepchenko Friday in quarterfinal action at the Bank of the West Classic.
Radwanska needed 2 hours, 14 minutes to dispose of the sixth-seeded American by a 7-6 (7-2), 3-6, 6-3 margin.
Another American awaits Radwanska in the semifinals in the form of fourth- seeded Jamie Hampton, who straight-setted Russian qualifier Vera Dushevina 6-4, 6-3 to move past the quarterfinals.
Third-seeded Dominika Cibulkova of Slovakia also advanced in straight sets Friday, earning a 7-5, 6-3 decision over seventh-seeded Urszula Radwanska.
Cibulkova will take on Sorana Cirstea in the semifinals after the fifth-seeded Romanian breezed past Olga Govortsova 6-3, 6-2 in just over an hour.
The winner of this tournament will receive $125,000.