Radwanska, seeded seventh, hadn't beaten Wozniacki since their first meeting in 2007 but came out ahead 3-6, 5-7, 6-2 in a quarterfinal match Wednesday. She broke Wozniacki's serve eight times. One break was in a 12-point game to win the second set and she broke at love to finish off the upset.
Wozniacki didn't win half the points off her first serve and lost 53 percent of the points on serve in the 2-hour, 38-minute match.
She'll now be watching world No. 2 Petra Kvitova, who swept aside Daniela Hantuchova 6-0, 6-4 in her quarterfinal Wednesday. If Kvitova wins the Apia International title, she will take over the world No. 1 ranking. Against Hantuchova, Kvitova lost only 12 points on serve and won 58 percent of the points when receiving.
Also Wednesday, third-seeded Victoria Azarenka defeated No. 8-seeded Marion Bartoli 7-5, 6-3 behind seven service breaks and No. 4-seeded Li Na, the tournament defending champion, got by Lucie Safarova 6-2, 7-6 (7-3).
Kvitova will go against Li in the semifinals. They have split their two previous meetings, both of which were last year. Azarenka has won five of her eight matches against Radwanska.