NEW YORK --- It's not quite the case that 17-year-old Melanie Oudin and her family knew for sure she would get this far, this fast.

Not when Melanie was 7, hitting buckets of tennis balls with Grandma Mimi back home in Marietta, Ga. Not a couple of years later, when Melanie and her twin sister began taking lessons together. And certainly not when Melanie lost her first two Grand Slam matches.

Still, there was Oudin at the U.S. Open on Thursday, ranked all of 70th, dealing with a painful leg and an overwhelming occasion on a supersized stage -- and stunning No. 4-seeded Elena Dementieva 5-7, 6-4, 6-3 to set up a third-round match against 2006 champion Maria Sharapova.

All the while, Oudin sported this word stamped near the heel of her pink-and-yellow sneakers: "BELIEVE."

The idea for that bit of inspiration came from her boyfriend, Austin Smith, a 15-year-old who helped Melanie prepare for her Arthur Ashe Stadium debut by practicing together in the 23,763-seat arena at 9:30 a.m. on Thursday.

"During the match, I had confidence, and, I mean, I was right there with her the entire time," Oudin said. "She wasn't blowing me off the court. She wasn't hitting winners left and right on me."

Don't, though, get the mistaken idea that Dementieva played poorly or showed the sort of nerves she has in the past. Dementieva played rather well -- displaying the stinging groundstrokes that carried her to two Grand Slam finals and an Olympic gold medal -- and graciously gave credit to Oudin, who now will face the scrutiny that comes with being the "Next Great American Hope."

"It's just the beginning," Dementieva cautioned, "but it looks like she has a good future."

Next comes what figures to be a stern test against three-time major champion Sharapova, who eliminated another 17-year-old American, Christina McHale, of Englewood Cliffs, N.J., 6-2, 6-1 at night.

No. 1 Dinara Safina turned in her second poor performance of the week before hanging on to edge 67th-ranked Kristina Barrois, of Germany, 6-7 (5), 6-2, 6-3.

Winners on the men's side included 2007 runner-up Novak Djokovic, and four Americans: 276th-ranked Jesse Witten, 55th-ranked John Isner, No. 21 James Blake and No. 22 Sam Querrey.