Radwanska, the No. 3 seed this week, defeated 10th-seeded Caroline Wozniacki 6-4, 6-3. Radwanska dropped serve once in each set but had a total of five breaks in advancing to Friday's semifinals.
She was the only higher seed to make it out of Thursday's play. World No. 1 Victoria Azarenka didn't even make it to the court. She complained of dizziness before her scheduled match and retired, giving fifth-seeded Angelique Kerber a walkover win.
Eighth-seeded Samantha Stosur took a tight 6-4, 7-6 (12-10) decision over second-seeded Maria Sharapova. Stosur had beaten Sharapova just once in 11 career meetings but finished off both break-point chances she had in the first set. Both players had three breaks before the 22-point tiebreaker ended the match.
Nadia Petrova, the No. 17 seed, survived a 2 1/2-hour battle with sixth-seeded Sara Errani to a 3-6, 7-5, 6-3 victory. Petrova ended up with six breaks, including four in the final set.
Radwanska is to play Kerber in the semifinals. A win at Wimbledon gave Radwanska a 3-2 series lead over Kerber. Petrova had won five of her eight previous matches against Stosur. They have split two meetings in 2012.