Serena Williams crashed out of the US Open semi-final, losing 2-6 6-4 6-4 to unheralded Italian Roberta Vinci, ending the American's dreams of a calendar Grand Slam.
World number one Williams was bidding to become only the fourth woman to win all four majors in the same year and had looked unstoppable in New York.
It marked the first time she lost to unseeded Vinci in five career meetings and Friday's result at Flushing Meadows marked a huge upset.
Vinci, ranked 43rd in the world, had never gone further than the quarter-finals of a major tournament before but the 32-year-old came from a set down to win.
It means Williams' run of 33 consecutive grand slam victories comes to an end while Vinci will now play fellow Italian Flavia Pennetta in Saturday's final.
"I thought she played the best tennis in her career," said 33-year-old Williams. "You know, she's going for it at a late age.
"Actually, I guess it's inspiring. I think she played literally out of her mind."
After wrapping up her momentous win, Vinci broke down in tears, dumbfounded as she struggled to speak during her on-court interview.
"It's an incredible moment for me," Vinci said after an epic two-hour contest.
"It's like a dream, I'm in the final, I beat Serena, it was an incredible match.
"I tried to stay focused, not to think about the match or about Serena, she is an incredible player. It is the best moment of my life."
Vinci added: "I am sorry for the American people, for Serena, for the Grand Slam, but today is my day, sorry guys."
Vinci had been knocked out in the first and second rounds at all three major tournaments this year but after a slow start, the wily Italian unsettled her opponent with slice, angle and variety of shot.
Williams opened up with an ace, one of 16 she served in the match, but four baseline errors gave Vinci an early break and a 2-1 lead.
The top seed switched her racket at the changeover and it seemed to do the trick, as Williams broke back, winning five out of the next six games to take the set with ease.
Vinci, however, refused to be discouraged as she snatched the first break again in the second set and this time held on, surviving a break point at 5-4, to serve out and force a decider.
Williams vented her frustration, bashing her racket at the changeover for which she picked up a warning from the umpire, but she seemed to recover as she stormed into a 2-0 lead.
Vinci, however, would not lie down and a Williams double fault handed the break straight back to the Italian, who was growing in confidence with every point won.
Williams cranked up the volume at 2-2, greeting every point with a violent scream and clench of the fists, but two games later Vinci responded in kind, cupping her ear to the crowd and pointing to her chest after finishing a scintillating point with a volley.
The drama was far from over as Vinci hustled, harried, chipped and chiselled her way to a break of serve at 3-3 and then held serve to sit one game away from victory.
Williams held to put the pressure back on her opponent but Vinci showed nerves of steel at 5-4, producing two superb half-volleys to serve out and complete the most unlikely of triumphs.
Earlier in the day in the first of the rain-delayed semi-finals, Flavia Pennetta crushed Romanian second seed Simona Halep 6-1 6-3 with a stunning upset that put the Italian into her first grand slam final.
Pennetta, 33, entered the contest as the clear underdog but the 26th seed showed her experience and was not overwhelmed on the big stage having reached at least the quarter-finals at Flushing Meadows in six of the last seven years.
"It's amazing. I didn't think to be so far in the tournament," said Pennetta, who will play either compatriot Roberta Vinci or top-seeded Serena Williams in Saturday's final. "Today I think I played really well."
