NEW YORK  —  She sat there in shock. Then, the tears started falling.

Believe it or not, 17-year-old Melanie Oudin is the toast of the town at the U.S. Open.

Gritting her way through a shaky third set, the 70th-ranked player from Marietta, Ga., pulled off her second upset of the Open on Saturday, defeating a more-seasoned, more-famous, more-moneyed opponent — 29th-seeded Maria Sharapova, 3-6, 6-4, 7-5.

“I don’t even know what to say right now,” Oudin said, choking back tears in her postmatch interview in Arthur Ashe Stadium. “Thank you so much for cheering for me.”

Sharapova, who has won this tournament once, usually gets those cheers. But on this cloudless day in Queens, the fans were rooting for a new potential queen — the one who stamped the word “Believe” on her shoes, but probably didn’t see this coming so soon.

“My goal was to make the top 50,” she said. “But if I keep playing like this, who knows? Hopefully, I can get as high as anything.”

She added this upset to one over No. 4 Elena Dementieva in the second round and a win over former No. 1 Jelena Jankovic earlier this year at Wimbledon.

Sharapova, though, was the biggest name in the bunch. Oudin’s confidence is growing as quickly as her resume, and suddenly, it does seem like anything is possible.

“Yeah, why not?” Sharapova said. “I think with experience and playing tournaments and being in situations where she’s playing these kind of matches, considering her age, she certainly has a great amount of potential.”

Oudin’s fourth-round match is against No. 13 Nadia Petrova of Russia, though there’s a sense she may have already knocked out the two toughest players on her side of the draw. No. 5 Jankovic is also gone, along with No. 11 Ana Ivanovic. No. 1 Dinara Safina is still there, but she has been playing poorly.

The Williams sisters are on the other side of the draw and it may not be too early to dream about the third-best American, Oudin, going against one of the two best for the U.S. title.

“I learned, once again, proved to myself that I can compete with these top girls,” Oudin said. “And if I believe in myself and my game, then I can beat them.”

In men’s play, No. 1 Roger Federer extended his winning streak to 37 at the U.S. Open, overcoming some shaky play for a 4-6, 6-3, 7-5, 6-4 victory over No. 31 Lleyton Hewitt.

It was Federer’s 14th straight victory over Hewitt, a former No. 1 who won the U.S. Open in 2001.

“I just had to believe that I could still turn this around,” Federer said. “And with the great streak I have against him, I knew that if I could get back into the match then I could get back on a roll, because I’ve done it so many times against him.”

Other winners on the men’s side included 15th-seeded Radek Stepanek, 10th-seeded Fernando Verdasco, eighth-seeded Nikolay Davydenko, and fourth-seeded Novak Djokovic, who ended 276th-ranked American Jesse Witten’s surprising run. Also gone is 22nd-seeded Sam Querrey, a 6-2, 7-5, 6-7 (6), 6-1 loser to No. 12 Robin Soderling.

Oudin and Sharapova followed Federer onto the show court but Sharapova did not put on a headliner’s performance.

She served 21 double-faults — the equivalent of five-plus games — committed 63 unforced errors and clearly hasn’t rounded fully into form after nearly 10 months off with a shoulder injury that forced her to miss the trip to Flushing Meadows last year.

Sharapova and Oudin traded three breaks each through the first eight games of the third set, then Oudin got a fourth break to go ahead 5-4. She responded by holding serve, closing the match with a cross-court winner off a short counterpunch from Sharapova.

Oudin dropped her racket and choked back tears, shook hands with Sharapova and walked to her chair, shaking, clearly having trouble believing what had taken place.

But, yes, that happened.

“Someone asked me this question at Wimbledon, ‘How I would describe the whole experience,'” she said. “There’s not really one word. Everything about it is just unbelievable. But basically I love to play tennis, and that’s why I’m here. I’m loving it.”