Petrova and Kirilenko claimed a 6-1 6-4 victory on Louis Armstrong Stadium court for their first victory over the American sisters, to reach the quarter-finals.

London – Serena Williams admits she is dreading a potential Olympic semi-final showdown with sister Venus after sweeping into the last eight with a 6-1, 6-0 rout of Russia's Vera Zvonareva on Wednesday.

Williams is bidding to win a singles gold medal for the first time and the American fourth seed remains on course to achieve her aim after a third successive demolition job at the All England Club.

The 30-year-old, who faces former world number one Caroline Wozniacki or Slovakia's Daniela Hantuchova in the last eight, had lost just nine games in her first two matches and she needed only 51 minutes to crush Zvonareva in an almost perfect display under the Wimbledon Centre Court roof.

But the biggest obstacle to Serena's gold dreams is likely to come from her own family as Venus, a singles gold medallist at the 2000 Games in Sydney, has also been in superb form this week and was due to play Germany's Angelique Kerber in the last 16 later on Wednesday.

If Venus wins that match the sisters will be one more victory each away from clashing in the semi-finals and Serena said: “I watched her the other day and I said, 'Serena, you need to play better or she's getting the gold'.

“I hate to practice with her. We were practicing here the other day and she killed me. I walked off the court.

“I told (USA coach) Mary Joe (Fernandez), 'I can't practice with her'. She was hitting winners left and right. I was like, Are you serious? I just left. It was too much.”

Williams, a two-time doubles gold medal winner with sister Venus, thrashed Zvonareva in the 2010 Wimbledon final and this match was even more one-sided.

It took just two minutes to determine the course of the match as Serena, a 14-time Grand Slam winner, easily broke the 13th seed in the first game.

There was never any doubt who would go on to win after that emphatic opening, but even Serena was shocked by how well she had played.

“I was nervous going into the match. I had a bad practice,” she said. “I was thinking, 'Gosh, I'm stressed out'.

“I had no idea I would play like this. I was a little surprised.”

Serena has carried her dominant Wimbledon form into the Olympics and the 14-time Grand Slam winner believes she might be playing even better now.

“I think I played better today and even in my second round than any match I played at Wimbledon,” she said.

“I was just playing unbelievable (against Zvonareva). I felt good. I was relaxed.

“I felt like 'I'm here to have fun, I have nothing to lose. No pressure on myself'.” – Sapa-AFP