Wimbledon champion Serena Williams cemented her status as the favourite for Olympic singles gold with a 6-1 6-0 victory over Russia's Vera Zvonareva that put her in the quarter-finals.

The USA player, seeded fourth, needed only 51 minutes to cruise through under the Centre Court roof against the bronze medallist from Beijing 2008.

Williams already has two gold medals to her name in women's Doubles with sister Venus.

If she matches that in Singles she will join Steffi Graf in winning all four grand slam titles and taking Olympic gold in her career.

In the last eight Williams will meet either eighth seed Caroline Wozniacki or Slovakia's Daniela Hantuchova.