World number one Caroline Wozniacki suffered a surprise fourth-round defeat by Germany's Andrea Petkovic in the Sony Ericsson Open on Monday.
Petkovic played positive attacking tennis in the Florida sunshine at Key Biscayne to move into the last eight with a 7-5 3-6 6-3 victory over the top-seeded Dane.
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The German of Serbian descent, who has just one WTA tournament win to her name, saved 12 of 17 break points against Wozniacki.
Russian Maria Sharapova eased past Australian Samantha Stosur 6-4 6-1.
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