BEIJING (AFP) - Top seed Roger Federer avenged his Athens 2004 humiliation with a convincing win over Tomas Berdych as he remained on course for an Olympic final with Rafael Nadal on Wednesday. Federer was broken in each set but came roaring back each time to end it 6-3, 7-6 (7/4) and erase memories of the second-round shock by the Czech which left him in tears four years ago. "I'm very happy with the way I played. I haven't lost to him since the Olympic Games," Federer said." He's always dangerous - you can see how hard he hits the ball."Earlier Nadal and Novak Djokovic ended Russian involvement in the men's singles with straight-sets wins to also reach the last eight. Nadal saw off Igor Andreev 6-4, 6-2 while Djokovic beat 13th seed Mikhail Youzhny 7-6 (7/3), 6-3 as both moved closer to a first Olympic title."I'm playing close to my best level. I beat a very tough player today," said the Spaniard. "My feeling is go on court and try to play my best tennis all the time."Nadal will meet Jurgen Melzer in the last eight after the Austrian ended the giant-killing run of Taiwan's Lu Yen-Hsun 6-2, 6-4. Third-ranked Djokovic will play either seventh seed David Nalbandian or Gael Monfils for the prize of meeting Nadal in the semis. Athens bronze-medallist Fernando Gonzalez and Paul Henri-Mathieu of France also came through against Olivier Rochus and Nicolas Kiefer respectively. Meanwhile, China's Li Na delighted home fans with a 4-6, 6-2, 6-0 victory over Estonia's Kaia Kanepi. She will face 2000 singles and doubles champion Venus Williams in the quarter-finals."I couldn't find my rhythm at first - I was completely unfamiliar with her," Li said. "But finally I got my chance. I feel lucky to play on my home court and with so many Chinese fans behind me." However, there was heartbreak for Wimbledon semi-finalist Zheng Jie, who went down 6-4, 6-3 to Russian sixth seed Dinara Safina. Federer and Berdych traded breaks in their first set before the Swiss again got ahead and served out the set with an ace. He netted a backhand to go a break down in the second but hit back in game five and dominated the tie-break, finishing it off with an ace and a service winner. Federer, who finished fourth in 2000, will face either James Blake or Gilles Simon in the quarters. Incoming number one Nadal broke Andreev at 3-3 and saved four break points when serving for the set with a series of unreturnable deliveries. The setback clearly affected Andreev and Nadal broke twice before taking the match with another big serve, making it four in a row against the 25-year-old. Nadal is bidding for his eighth title this year after his fourth French Open crown and first Wimbledon win boosted his career trophy total to 30. He is playing his first Olympic singles tournament after appearing as a little-known doubles player four years ago in Athens. Nadal's half of the draw has been eased by the exit of world number six Andy Murray, who was shocked in round one by Taiwan's Lu. Defending champion Nicolas Massu has also been eliminated. Nadal, Federer and Djokovic are all bidding to become the first top-five men's singles gold-medallist. Nadal replaces Federer in the top ranking on Monday after more than three years at number two.