A devastating Roger Federer is proving he shouldn't be written off yet.

The Swiss tennis great avenged his second-round defeat at the Athens four years ago by rolling past Tomas Berdych of the Czech Republic 6-3, 7-6 (7-4) Wednesday to reach the quarterfinals.

His archrival, Spain's Rafeal Nadal, is on track as well, demolishing Igor Andreev of Russia, 6-4, 6-2.

Roger Federer of Switzerland applauses after defeated Tomas Berdych of the Czech Republic during their 2008 Beijing Olympic Games men's singles third round tennis match in Beijing on August 13, 2008. [Agencies]

"I am playing close to my best level," Nadal said. "My goal is try to continue playing like this."

World's two biggest stars could meet in the final on Sunday, the day before Nadal is set to end Federer's five-year reign as world No 1 in the rankings.

Federer now plays James Blake, top hope for the United States who beat Gilles Simon of France 6-4, 6-2.

The world No 3 Novak Djokovic, who has been struggling to regain his form since May, saw off Mikhail Youzhny of Russia 7-6, 6-3.

In the women's, Venus Williams' hopes of a second Olympic singles gold remained aggressive after easing into the quarterfinals by beating Victoria Azarenka of Belarus 6-3, 6-2.

Williams, seeded seventh, is seeking to add to her Olympic medal collection after winning the singles and doubles at Sydney in 2000.

"It's only every four years, so now is the time to really play well," she said.

Williams will now play home favorite Li Na, who beat Estonia's Kaia Kanepi 4-6, 6-2, 6-0 to become the first Chinese player to reach the last eight of an Olympic tennis tournament.

"I wanted to win but I played conservatively and I couldn't find my rhythm at first, but I finally got my game," Li said.

Fans waved Chinese national flags and chanted "Go China" throughout the match though sometimes referees found it hard to stop the spectators.

"I feel very grateful for what my fans did today. They cheered with so much passion and many of them used my hometown dialect. It felt great to play with them around," Li added.

Talking about her next round clash with Williams, Li said: "I'll try to push her hard and give her a hard time. The whole world knows she is a very powerful player, but I have defeated top 10 players several times before, so I won't write myself off in the Olympics."

Another Chinese player, Zheng Jie, failed to go forward after losing to Diara Safina in straight sets.

This is Zheng's third consecutive loss to the Russian and their last clash was at the French Open in May when Safina demolished Zheng 6-2, 7-5.

Zheng became the first Chinese to reach a Grand Slam semifinal at Wimbledon this year, capping a successful return from an ankle injury, which caused her to miss six months in 2007, but Safina's solid groundstrokes eliminated Zheng's hope.

"She is in great shape, and she didn't make a mistake," said Zheng. "But it is not the end of the world for me, as I can totally focus on my doubles event right now."