Stanford: No. 5 seed Yanina Wickmayer beat No. 2 Marion Bartoli 6-3, 6-2 for the first time in four meetings, earning a trip to the Bank of West Classic semi-finals on Friday.
Wickmayer next faces American Coco Vandeweghe, who knocked off Urszula Radwanska of Poland 6-4, 6-4 to make the semi-finals of a WTA Tour event for the first time.
The 37th-ranked Wickmayer recorded her third career top-10 victory with the win over 10th-ranked Bartoli, and the first of the season.
Vandeweghe, ranked 120th, earned a spot in the main draw after three players withdrew due to injuries.
No. 3 seed Dominika Cibulkova of Slovakia also lost, falling 6-7 (5), 6-2, 6-0 against Sorana Cirstea of Romania.
Cirstea will play the winner of a late match between Serena Williams and Chanelle Scheepers.