Signaling his recent tailspin may be over, Federer avenged a defeat four years ago at the Olympics by beating Tomas Berdych of the Czech Republic 6-3, 7-6 (4) on Wednesday to reach the quarterfinals.

It was Federer's biggest victory since he lost to Rafael Nadal in an epic Wimbledon final last month.

Federer wept after losing to Berdych in the second round at the Athens Games in 2004. This time he was shouting "Yes!" and punching the air after he smacked a service winner on match point to finish off Berdych.

"Of course you have memories of such a big tournament and losing," Federer said. "He's a good player. So I'm very happy with this win, because I think this was the first true test in this tournament."

Rafael Nadal too advanced into the quarterfinals at the Olympics on Wednesday, digging out of a hole in a pivotal service game and beating Igor Andreev of Russia 6-4, 6-2.

The No 2-seeded Nadal is seeking his first Olympic medal to complement the French Open and Wimbledon titles he has won this year. No 3 Novak Djokovic, who could meet Nadal in the semifinals, beat No 13 Mikhail Youzhny of Russia 7-6 (3), 6-3.

Venus Williams, playing her first tournament since winning Wimbledon for the fifth time, reached the quarterfinals by beating No 12 Victoria Azarenka of Belarus 6-3, 6-2. Williams, seeded seventh, is seeking to add to her medal collection after winning the singles and doubles at Sydney in 2000.

Nadal played his third-round match on Court 1, which resembles a bull ring, and the Spaniard looked right at home as he wore down Andreev from the baseline. The 4,000-seat stadium was packed, and because of heavy haze the lights were on despite a 4 pm start.

Nadal broke for a 4-3 lead and served for the first set three games later. He fell behind love-40 and faced four break points in the game but overcame them all, with Andreev hitting a service return out each time.

In the second set, Nadal raced to a 4-0 lead. He closed out the match with a service winner, then punched the air in triumph. Nadal is assured of climbing to No 1 in the rankings next week, ending Roger Federer's reign.

Federer could meet Nadal for the gold medal on Sunday in a rematch of their epic Wimbledon final.