Serena Williams will face world number one Victoria Azarenka in the semi-finals of the Olympic women's singles after beating Caroline Wozniacki.
The American, who has two doubles gold medals, won 6-0 6-3 as Azarenka of Belarus beat Angelique Kerber 6-4 7-5.
Russia's Maria Sharapova overcame Kim Clijsters and plays compatriot Maria Kirilenko, who upset Petra Kvitova.