American Jennifer Capriati bettered rival Serena Williams 2-6 6-4 6-4 to reach the last four of the US Open.
Williams stormed 3-0 ahead with a powerful combination of serves and backhands, and Capriati could find no answer as Williams claimed the set.
But the third seed let her focus slide in the second and Capriati capitalised on her errors to level the match.
A bad line call disrupted Williams in the decider's first game, and Capriati broke and stayed firm to go through.
Capriati, who has never won the title at Flushing Meadows, will now meet Elena Dementieva on Thursday for a place in the final.
"She came out firing and I started tight but I just tried to stay with her," said a delighted Capriati.
"I just didn't want to let it slip away.
"It shows how good life is, you keep getting chance, after chance, after chance. I
can't stop this now."
The loss for Williams means it is the first season since 1998 that either her or sister Venus have failed to win a Grand Slam.
And the 22-year-old believes the umpire's mistake at the start of the third set cost her a place in the semi-finals.
"I'm very angry and bitter right now," said the third seed. "I feel cheated and robbed.
"Not only was the ball in, it wasn't even near the line.
"But I'm not making excuses. I probably should have closed her out in the second
The 22-year-old looked to be on her way to an easy victory as she effortlessly wrapped up the opening set.
But she failed to carry that momentum forward, gifting Capriati a series of unforced errors and a 2-0 lead in the second.
Neither could the double US Open champion convert her break points on Capriati's serve.
The eighth seed was 30-40 down in the 10th game but Williams scuffed a service return and dumped the ball into the net to see Capriati level the match.
Williams finally unravelled in the decider thanks to a dreadful line call which handed Capriati the break at 1-0.
The third seed managed to break straight back in front of a fired up crowd but she could not regain her consistency.
More wayward shots from Williams allowed Capriati to notch up the third straight break in the decider - won with a perfect forehand down the line.
The New-York born Capriati's nerves fluttered as she served out for the match.
The 28-year-old twice missed two match points but it was Williams who wildy conceded the match with her over-anxious play.