Sports

It’s finally midnight for Cinderella

Melanie Oudin had Caroline Wozniacki just where she wanted, losing her fourth straight opening set, luring the more experienced Dane into the American’s perverse web.

This Harriet Houdini had not merely escaped Elena Dementieva, Maria Sharapova, Nadia Petrova, but pounded them down over three sets like they were the 17-year-olds and Oudin was the old pro. Thus, visual evidence of 18 unforced errors in the 2-6 first set wasn’t shaking the kid’s confidence, not at all.

“Believing was my key thing going into these matches, knowing I could compete with these women and beat them,” she said again last night, and why would a match against the least accomplished player of the four be any different?

At 1-1 in the second set, a backhand crosscourt winner had Wozniacki down 15-40, opened up again the path to the U.S. Open final as wide as has been America’s arms to a 5-foot-5 Georgian gnat.

But Wozniacki responded with a forehand winner, played some serious defense until Oudin hit another long forehand, took the advantage when she returned wide, then apparently had won the game, when Wozniacki’s backhand caught netcord.

It hung, then dropped over regardless.

Arthur Ashe Stadium got so quiet, you could hear a dream drop. The karma was gone and soon, so was America’s sweetheart from the 10 best days of her young life.

Serving at 1-2, Oudin failed to convert three ads, finally hit into the net off another deep forehand by the older, clearly looser player.

“She plays incredible defense, doesn’t give you anything for free,” said Oudin.

Indeed, the non-plussed ninth-seed, just 19 herself and in her first Slam quarterfinal, too, won going away, 6-2, 6-2, to earn a date tomorrow with another 19-year-old first-time semifinalist, Yanina Wickmayer.

Yesterday’s news — Kim Clijsters and Serena Williams — will slug it out in the other semi; the winner of that one surely to get a 10th straight U.S Open women’s final over in straight sets on Saturday night.

Nevertheless, opportunity knocked to get there, and Oudin, with tears in her eyes as she came to the net to congratulate Wozniacki, knew it.

“I’m a perfectionist, losing isn’t good enough for me,” she said. “But then that was right after I had come off.

“I really think about it, I have had an incredible two weeks, should be proud of myself. I never thought I’d play Maria Sharapova on Arthur Ashe Stadium at the U.S. Open this year. Definitely did not see that coming.”

Neither did Sharapova, who like Dementieva, then Petrova, wilted under the relentlessly placed forehands of the mighty mite.

“You know, it’s kind of hard to explain how I’ve done it,” Oudin had said at one point, but not really, considering the history of collapses under adversity by so many underachieving women.

Not Wozniacki, who unlike a frazzled Oudin, looked like the next good thing last night. Oudin can have a top-15 career just by keeping the ball in play but Slam contention will depend upon how well she learns to think the game.

Last night, she didn’t do well at all, going for too many winners from too far back of the baseline.

Oudin’s best points were off a backhand drop that would have made her idol, Justine Henin, proud, but 43 unforced errors to 20 were far too many to overcome, turned the kid just another baseline banger unable to figure out how to keep herself alive while struggling with a bread-and-butter shot.

She will move up in the rankings perhaps as high as No. 43, a long way from No. 70 where she started this tournament. And yet an appropriate number measuring how far Oudin has to go.

jay.greenberg@nypost.com