NEW YORK — Melanie Oudin missed the junior prom.

Skipped homecoming, too.

And the 17-year-old isn't spending a lot of time hanging out with pals at the mall, either.

Then again, none of the other kids back in Marietta, Ga., is preparing to play in the U.S. Open quarterfinals Wednesday night.

"She doesn't do any of that kind of stuff — and she's OK with it," Katherine Oudin said after sobbing in the stands when her twin sister pulled off a fourth consecutive upset victory at Flushing Meadows.

"I know she misses the normal life a little, but she does not regret it at all. Zero," Katherine said. "She's totally OK with it, because she knows this is what she's wanted her entire life."

That's a relative term, of course. When your "entire life" encompasses 17-plus years — and you began playing tennis at 7, hitting balls out of a bucket with Grandma Mimi — you haven't exactly been waiting forever for success. Indeed, Oudin is the youngest U.S. Open quarterfinalist since Serena Williams in 1999.

As the twins' mother, Leslie, put it: "All of this has come so quickly."

Sure has. A year ago, Oudin was ranked 221st and lost in the first round in New York. She never had won a Grand Slam match until Wimbledon in June. Nowadays, she high-fives security guards on her way into the locker room.

Everything is "awesome" and "cool," and she's "freaked out." Her stunning win over three-time Grand Slam champion Maria Sharapova? "I just had a blast."

This is where Oudin wanted to be, dating to when she and her sister would play "mini-tennis" in the cul de sac by their home, piling up jackets as a makeshift net. Or when the twins would hit balls against the garage door until Katherine would get bored, leaving Melanie out there alone — thwack! thwack! thwack! — until Mom or Dad ushered her inside at nightfall.

Or when Melanie would watch the Williams sisters on TV and proclaim that she wanted to play in those big arenas, too. Look at her now: There are still shots to be made and matches to be won, for sure, but there is a possibility Oudin could play Serena Williams in Saturday night's U.S. Open final.

Oudin has been sharing a king-sized bed with Mom in a Manhattan hotel — until, that is, they had to switch hotels because they hadn't reserved the room for long enough. Hey, who would have thought she'd still be playing? They've been waking up together when the alarm goes off, then going their separate ways: Melanie hops in a courtesy car provided for players; Mom waits in line for a shuttle bus to the tournament site in Queens.

Not that this wild ride is getting to the kid's head.

She vows to keep doing some landscaping work around the grounds at the tennis club where she still practices with the same coach she's had since she was 9.

"Just because all of this is happening, it's not like I'm going to change (as a) person," Oudin said. "I just love to play tennis, and I'm doing well. And I'm winning. That's the only thing that's changing."

Well, that and all of the attention she's getting. Unaccustomed to being recognized by strangers, Oudin now needs security guards to navigate hordes of autograph-seekers on her way to the practice courts. Crowds gather in the lobby of her hotel. A photo op in Times Square the other day got unruly. The evening news shows at ABC, CBS and NBC all sent crews to interview Oudin after her latest win.

"It's going to take a while to get used to it," said her coach, Brian de Villiers. "She's used to going where she wants, when she wants. It's strange for this little kid."

Oudin's age and newcomer status are only a couple of the many reasons she has become the focus of the year's last major tennis championship.

For one thing, she's an American at the American Grand Slam tournament, providing hope for the future of the sport in a country that boasts the Williams sisters at Nos. 2 and 3 in the rankings — but then no one else until Oudin at No. 70. This also happens to be the first U.S. Open in history with zero U.S. men in the quarterfinals.

Oudin's story is also compelling because of the players she has beaten — and how she beat them.

She's the ultimate underdog. The worst-ranked of any of her opponents so far was No. 36 Anastasia Pavlyuchenkova in the first round. Otherwise, Oudin dismissed No. 4-seeded Elena Dementieva, No. 13-seeded Nadia Petrova and former No. 1-ranked Sharapova. All are somewhere between 3 and 8 inches taller than the 5-foot-6 Oudin. And all, coincidentally, are Russians, prompting one reporter from that nation to preface a question he posed to Oudin by noting, "Basically, you managed to crush them."

Actually, not exactly. In each of her last three wins, starting against Beijing Olympics gold medalist Dementieva, Oudin lost the first set before coming back to defeat the more experienced, more accomplished player across the net.

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

Oudin can't necessarily outhit anyone. Or outserve them, rarely approaching 100 mph and accumulating a paltry total of four aces through four matches.

What Oudin does is outhustle other players, scurrying this way and that, her pink-and-yellow sneakers — which feature, at her 15-year-old boyfriend's suggestion, the word "BELIEVE" stamped near the heels — squeaking with every tiny step.

"Mentally, I'm staying in there with them the whole time, and I'm not giving up at all," Oudin said. "If they're going to beat me, they're going to have to beat me, because I'm not going to go anywhere."

She decided at 12 she wanted to be home-schooled so she could focus squarely on tennis. Katherine, meanwhile, has designs on being a doctor and attends private school, playing on the tennis team there and entering national junior tournaments.

After Melanie's first-round match last week, Katherine and their younger sister flew home to Georgia because school was starting. But Melanie kept on winning, so Katherine and their father came back in time for Monday's victory.

"Right now, I think she'll play Serena in the finals," Katherine said, "and we're not going anywhere until that happens."

Nice. A little trash-talking from the twin.

Clearly, this is all so new to the whole family.

And clearly, Oudin herself is so new to all of this. So much so that her quarterfinal opponent, No. 9-seeded Caroline Wozniacki of Denmark — who is all of 19 — joked about not being quite sure how to say Oudin's name.

For the record: It's "oo-DAN," on account of her father's French ancestry. Wozniacki is hardly the only one having trouble, though. Chair umpires and plenty of others bungle the pronunciation, too.

"Sometimes they get it wrong," Oudin said, "but I don't try to tell them anymore."

Not to worry. Keep this up, and it will be a household name soon enough.