After beating Petrova, Oudin huddled with her coach, Brian de Villiers, trying to figure out how to squeeze in various media obligations with necessary tasks such as eating something and getting treatment for her heavily wrapped left thigh.
"That was her first realization that she's big-time, that it is going to be scary sometimes," Katherine said. "I'm surprised that she's held it together as well as she has."
On the court, the situation seemed bleak when Petrova, already up a set, was serving at 4-3, 40-15 in the second. One more point, and Petrova would be a game from the win. But Petrova netted a forehand for 40-30, and on the next point, Oudin blocked back a 112 mph serve, then ended an 10-stroke exchange by smacking a forehand down the line.
"Unbelievable winner," said Petrova, who would never again be that close to victory.
"Winning that game kind of gave her a second breath," Petrova said. "She realized, 'OK, I'm back in the game.' And probably after winning previous matches pretty much in the same way, she thought, 'You know, I can do it again."'
Forced to hit extra shots because of the 5-foot-6 Oudin's ability to track down balls and sling them back, Petrova began to make more and more mistakes. During one key stretch early in the third set, Oudin won 11 of 13 points - and 10 were thanks to miscues by Petrova.
"She's on a roll. And she has nothing to lose," said Petrova, the fourth Russian in a row Oudin has beaten. "She goes, enjoys it, crowd is behind her. She's just having a blast out there."
"This," Oudin said, "is what I've wanted forever."
Not that forever is all that long in her case. She is, after all, "just 17" - as the lyrics go in the Beatles song reverberating through the Arthur Ashe Stadium sound system after her victories there.
Melanie and Katherine began hitting tennis balls out of a bucket with their grandmother at age 7, then began working with de Villiers at age 9. At about 12, though, Melanie decided she wanted to be home-schooled, so she could focus squarely on tennis. Katherine, meanwhile, plays in national junior tournaments, but has other interests, and is now a senior in high school.
As little kids, the sisters would play matches on a makeshift court, piling up jackets in their home's cul de sac to serve as a net until Mom or Dad said it was too dark to be outside.
They never pretended, though, that they were at Flushing Meadows or the All England Club. Those places seemed too far away at the time.
"It's not like we were saying, 'Oh, we're going to be there one day,"' Katherine said. "But Melanie's just always believed in herself. It's amazing."