Radwanska survived a difficult match in defeating Varvara Lepchenko 7-6 (7-2), 3-6, 6-3, moving closer to her third championship of the year.
Jamie Hampton will face Radwanska in the semifinals after dispatching qualifier Vera Dushevina 6-4, 6-3.
Urszula Radwanska, hoping to meet her older sister in the title match Sunday, came up short in the quarterfinals. No. 3 seed Dominika Cibulkova won a 7-5, 6-3 decision and will take on Sorana Cirstea, who defeated Olga Govortsova 6-3, 6-2.