Williams and Isner combined to Anderson and Scheepers 6-3 6-2 to secure victory in the mixed team event.

CNN: STORY HIGHLIGHTS

Williams, who has battled injuries and illness, came from a set down to beat Chanelle Scheepers 4-6 6-2 6-3 in the opening rubber.

CNN: STORY HIGHLIGHTS

Petrova will play Elena Dementieva in the last eight after her compatriot delivered a sure-footed performance to see off South African qualifier Chanelle Scheepers 6-1 6-3.

BBC: Venus Williams tumbles out of French Open

But 25th seed Anabel Medina Garrigues of Spain crashed out 1-6 6-4 6-0 to South African Chanelle Scheepers, while two-time grand slam champion Svetlana Kuznetsova, seeded 26th, lost 1-6 7-6 7-6 to Czech Iveta Benesova.

CNN: Serena returns with victory in Miami

World number 131 Scheepers had beaten Gisela Dulko, a player ranked 86 places above her, previously in her campaign as she became the first South African to reach the last 16 since Amanda Coetzer in 1997.

BBC: Venus Williams tumbles out of French Open

Eighth seed Victoria Azarenka was in excellent form in a 6-4 6-4 victory over Andrea Hlavackova of the Czech Republic and her next opponent will be South Africa's Chanelle Scheepers , who beat Russian Regina Kulikova 6-4 4-6 7-5.

BBC: Australian Open: Venus Williams labours to victory