Kerber, who beat Wozniacki in the finals at Copenhagen earlier this year, rolled over the sixth-seeded Wozniacki 6-1, 6-2 in 63 minutes. Kerber didn't face a break point and lost just 13 points in eight service games. Wozniacki was runner-up in the tournament last year.
That put Kerber into Friday's quarterfinals against third-seeded Petra Kvitova, who was a 6-2, 6-2 winner over Francesca Schiavone in an hourlong match. She lost only 12 points when serving.
World No. 1 Victoria Azarenka moved into the quarterfinals when, after Azarenka went up 6-2, 4-4, Andrea Petkovic retired. Mona Barthel earned a shot at Azarenka with a 6-3, 6-1 decision over Marion Bartoli. She didn't see a break point in the match.
Also Thursday, fifth-seeded Samantha Stosur slipped past defending champion Julia Goerges 6-2, 2-6, 6-3 and No. 8-seeded Li Na stopped Akgul Amanmuradova 6-4, 6-4.
Li goes against fourth-seed Agnieszka Radwanska and Stosur meets second-seeded Maria Sharapova in the other matches Friday.
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