MELBOURNE (AFP) - The Australian Open was blown wide open Sunday when top seed Jelena Jankovic crashed out while Roger Federer was forced to mount a memorable comeback to beat Tomas Berdych. The Serb's crushing 6-1, 6-4 defeat to French 16th seed Marion Bartoli put her alongside Ana Ivanovic and Venus Williams as high-profile early round casualties, raising further questions about her world number one status. Federer looked like he could join Jankovic after losing the first two sets to Czech Berdych, battling back to win 4-6, 6-7 (4/7), 6-4, 6-4, 6-2 and stay on course for a record-equalling 14th Grand Slam title. It was the first time Federer has come from two sets down since Miami in 2005, and he sees it as a good omen. "Tomas did so well and he pushed me to the limit," said the Swiss three-time champion. "I enjoy those kinds of fights because they don't happen very often, especially on Rod Laver Arena. I hope it is a good omen. "I feel in great shape, I feel like I could go another two sets." His next opponent is Argentina's Juan Martin del Potro, who recovered from a set down to grind out a 5-7, 6-4, 6-4, 6-2 win over fellow young gun Marin Cilic. There was also safe passage to the quarter-finals for American Andy Roddick, who will play defending champion Novak Djokovic. Djokovic held off 2006 runner-up Marcos Baghdatis 6-1, 7-6 (7/1), 6-7 (5/7), 6-2 in a match that started at 11:10 pm and finished at 2:26 am. With Jankovic, Ivanovic and Williams now gone, the first Grand Slam of the season has become one of the most open ever with Bartoli into a quarter-final against Russia's Vera Zvonareva, who beat countrywoman Nadia Petrova 7-5, 6-4. "It's obviously disappointing. Nobody likes to lose," said Jankovic, who looked lethargic as she tried to play her way into the match. "It was a tough day for me. You know, I had a slow start. I let my opponent completely come on top of me and play her game." She is now likely to lose her top ranking, but insisted it was not important. "It doesn't matter because it's just the beginning of the year, and there is many more tournaments to play," she said. Bartoli was ecstatic at the upset but said she always felt she could win. "I knew I could beat Jelena on a good day, it was just a matter of executing it, playing the right shot at the right time and not making too many mistakes," said the Frenchwoman, who made the Wimbledon final in 2007. Russian third seed Dinara Safina survived two match points to beat France's Alize Cornet 6-2, 2-6, 7-5 and will play Australian wildcard Jelena Dokic whose fairytale run continued with 7-5, 5-7, 8-6 win over Russia's Alisia Kleybanova. Safina appeared certain to follow Jankovic out when Cornet was serving for the match at 5-4 and 40-15, but she somehow clung on and hauled herself out of trouble. "I feel so lucky that I have the chance to play in the quarter-finals," said Safina. "This is the first time I have won when two match points were against me. "There are no easy matches here, there are no easy Opens." Argentina's del Potro became the youngest man in the last eight since Richard Krajicek in 1992 and has now reached two consecutive Grand Slam quarter-finals after last year's US Open. "Against Roger, he will be the favourite. I'll change nothing for the game," insisted the the 20-year-old. Seventh-seeded Roddick was in ominous form as he downed Spanish 21st seed Tommy Robredo 7-5, 6-1, 6-3. After battling out a tight first set, Roddick steamrolled his opponent in the second and third to send out a warning that he cannot be underestimated as he looks to add to his lone Grand Slam triumph at the US Open in 2003.