Radwanska reached the semifinals last week at the Bank of the West Classic before losing to Maria Sharapova.
This time she will meet Daniela Hantuchova, who was a 2-6, 6-4, 6-3 winner over Alisa Kleybanova.
Kleybanova had ousted top-seeded Jelena Jankovic in the second round. Radwanska will be trying for her first appearance in a championship match this year.
In the other half of the draw of a tournament played at the La Costa Resort and Spa, Flavia Pennetta eliminated second-seeded Samantha Stosur 6-4, 6-3 and Svetlana Kuznetsova was a 7-5, 6-2 winner over qualifier Coco Vandeweghe.
Vandeweghe was playing in the first quarterfinal match of her WTA Tour career.