Blinking back tears and ignoring the pain, the 17-year-old from Marietta, Ga., pulled off the biggest upset so far at the U.S. Open on Thursday, a 5-7, 6-4, 6-3 victory over No. 4 Elena Dementieva.
The win looks great alongside Oudin's victory over No. 6 Jelena Jankovic earlier this summer at Wimbledon, where she became the youngest player to make the fourth round since Jennifer Capriati in 1993.
Oudin, ranked 70th, played most of the third set with a heavy wrap on her left thigh, an injury that briefly reduced her to tears as she headed to the baseline to serve.
But the day ended with a loud shriek when she painted the backhand corner with her serve on her third match point at Arthur Ashe Stadium.
She could very well be booked there again later this week: Her next match will be against 29th-seeded Maria Sharapova or Christina McHale, another 17-year-old American.
"I don't even know what to say right now," Oudin said. "I'm so excited. You have no idea."
But, she conceded, she was hurting.
"I hit that last serve and, I don't know, it kind of just like sent a sharp pain through my leg," she said.
Dementieva, meanwhile, leaves Flushing Meadows with the more accomplished resume - 14 titles, 14 runner-up finishes, more than $12 million in career earnings - but still in search of her first Grand Slam title.
After her loss, Dementieva said she was impressed with America's new break-out player. The United States is always looking for depth in a talent pool that has long consisted of Serena and Venus Williams dominating at the top, with not too much beyond them.
"She was in the court, not afraid to play, playing very aggressively, really enjoying this atmosphere and the crowd support," Dementieva said. "It looks like she has a good future."
In the match next door at Armstrong Stadium, No. 1 Dinara Safina also stayed alive in the quest for her first major, but in ugly fashion - a 6-7 (5), 6-2, 6-3 victory over Germany's Kristina Barrois.
Safina won despite 38 unforced errors and 15 double-faults in her second straight uncomfortably close match.
She is ranked first despite having never won a major and she did little in this match against the 67th-ranked player in the world to cool the debate about whether she really belongs there.
No. 2 Serena Williams, going for her third major of the season, dispatched her opponent 6-1, 6-1 in 53 minutes in the final match Wednesday night in Arthur Ashe Stadium.
Safina, playing in a smaller venue for a Thursday matinee, needed 2 hours, 13 minutes, much of which looked like the 2 hour-25 minute display she put on in her three-set opener against Olivia Rogowska.
In fact, the endings of the first sets were identical: Safina double-faulting on set point to lose a 7-5 tiebreaker. And, as in the first round, Safina came back with a stronger second set to win 6-2.
The third set was 3-3 when Barrois' game collapsed. She missed an easy forehand on break point against her in the seventh game, then committed five unforced errors over the final two games before losing it with a double-fault on match point.
Barrois finished with 43 unforced errors, including 17 in the final set.
In other early action Thursday, men's No. 20 seed Tommy Haas of Germany defeated American Robert Kendrick. On the women's side, 13th-seeded Nadia Petrova advanced, while No. 30 Alona Bondarenko lost.
Others scheduled to play Thursday were Americans James Blake and Sam Querrey in the afternoon and Andy Roddick in the evening. Sharapova also was scheduled for Thursday night in Arthur Ashe Stadium.
The Williams sisters were also supposed to play their opening match in doubles, though Venus' knee has been bothering her and there were questions as to whether she would play in that event.