Melanie Oudin extended her remarkable run at the U.S Open to the quarterfinals with another thrilling victory, 1-6, 7-6 (2), 6-3 over 13th-seeded Nadia Petrova of Russia. The 17-year-old Oudin staved off two points that would have put her behind 5-3 in the second set, then rolled through the third, hitting corners with those underrated groundstrokes and taking advantage of 22 unforced errors by her more-seasoned, higher-ranked opponent. Rankings, like her age, however, are only numbers. The 70th-ranked player already had wins over No. 4 Elena Dementieva and No. 29 Maria Sharapova at Flushing Meadows, along with one over former No. 1 Jelena Jankovic this summer at Wimbledon. Now, she's knocked off No. 13. She has become the youngest American to move into the quarterfinals at America's Grand Slam since Serena Williams in 1999. 'I think this is going to do a lot,' Oudin said. 'I think it's good for American tennis.' Not so good for Russian tennis, though. All four of Oudin's wins have come against Russians and her next match could be against yet another. That's sixth-seeded Svetlana Kuznetsova, the 2004 Open champion and the only Grand Slam tournament winner left on Oudin's side of the bracket. After hitting a forehand to the corner for her 19th and final winner on match point, Oudin threw her racket in the air. This time, however, she didn't cry any tears of disbelief. Instead, it was twin sister Katherine sobbing in the stands. 'It's kind of hard to explain how I've done it,' Melanie said. 'Today, there were no tears because I believed I can do it. Now I know I do belong here. This is what I want to do. I can compete with these girls no matter who I'm playing. I have a chance against anyone.' Talk about heart. Oudin improved to 6-1 at Wimbledon and the U.S. Open this year when she's lost the first set. She is 17-4 overall this year in three-set matches. 'I don't actually mean to lose the first set,' she insisted. 'Sometimes, I just start off slowly. Maybe I'm a little nervous. Today, my timing was off a little. But I just totally forgot about it, started off the second set like it was a new match, and I started playing better.' Oudin won this match without serving a single ace, another indication she is not blowing anybody away with sheer power. Instead, it's footwork, technique, precision. Mostly, though, she is thriving in pressure situations that make so many others in the sport shrink away. 'You don't know if she's winning or losing,' said her father, John. 'She doesn't seem nervous out there -- and I don't know where that came from.' Maybe it's the shoes. They have the word 'Believe' stamped on them, and it's easy to see how those Oudin models could become top sellers in tennis shops across America soon. The teenager, schooled at home in Marietta, Ga., so she can concentrate on tennis, stung two forehand winners, including one when she was positioned completely outside the court, to take a quick 3-0 lead in the second-set tiebreaker. She also took advantage of three unforced errors and a double-fault from her 27-year-old opponent, who was trying to make her third Open quarterfinal. 'I have a feeling like I really didn't finish my job off on the court,' Petrova said. 'She came back, and after winning her previous matches in the same way, she probably thought, I can do it again.' In men's play, No. 1 Roger Federer beat No. 14 Tommy Robredo of Spain 7-5, 6-2, 6-2 for his 38th straight win at the U.S. Open. In the quarterfinals, Federer will face No. 12 Swede Robin Soderling, who he beat in the French Open final to complete his career Grand Slam. Soderling advanced when No. 8 Nikolay Davydenko of Russia retired with a leg injury at the start of the fourth set. American John Isner lost to No. 10 Fernando Verdasco of Spain 4-6, 6-4, 6-4, 6-4, assuring the men's quarterfinals will be without an American for the first time in history. In other women's matches Monday, Kateryna Bondarenko of Ukraine and Belgian Yanina Wickmayer won to set up a quarterfinal between two players ranked in the 50s. Little in the women's tournament has gone to form. Unseeded Kim Clijsters, into the quarterfinals in her comeback to pro tennis after a two-year break, is shredding up her side of the draw. Oudin is electrifying the other side. Four of the top five seeds are gone, with only No. 2 Serena Williams bringing any sense of stability to the proceedings. She has yet to be challenged in any of her four matches. 