Czech 10th seed Karolina Pliskova outplayed Serena Williams to reach the US Open final and end the American’s reign as world number one.
Williams, 34, double-faulted on match point to lose 6-2 7-6 (7-5), and Pliskova will face German second seed Angelique Kerber in the final.
The result guarantees that Kerber will overtake Williams at the top of the rankings after the US Open.
Williams had also hoped to win an Open-era record 23rd major singles title.
She remains tied with Steffi Graf for both Grand Slam titles, and the WTA record of 186 successive weeks as world number one.
“Karolina played great today,” said Williams, who revealed she had been hampered by a sore left knee since earlier in the tournament
“I think if she had played any less then maybe I would have had a chance. So I think I wasn’t at 100%, but I also think she played well. She deserved to win today.”
Australian Open champion Kerber beat Denmark’s Carolina Wozniacki 6-4 6-3 to reach her first US Open final, reports the BBC.
“It’s just incredible, it’s a great day,” said Kerber. “To be here in the final for the first time means a lot and to be number one in the world – it sounds amazing.”
Pliskova went into the match on a 10-match winning streak, and with the most aces on the WTA Tour this year, and it was that shot which carried the Czech to victory.
It took Williams 50 minutes to earn her first break point as the Czech nullified her returns, while attacking the American’s second serve.
That brought Pliskova two breaks as she raced through the first set in just 26 minutes, and the home crowd on Arthur Ashe Stadium urged on Williams as the six-time champion fell behind midway through the second set.
Williams sparked into life, finally breaking Pliskova’s serve – to love – but the anticipated comeback was cut short in the tie-break.
There were a few signs of nerves as Pliskova let a 3-0 lead slip but from 5-4 in front, Williams produced a forehand wide, a backhand long and a double fault to end with 31 unforced errors.
“I don’t believe it,” said Pliskova, who had never made it past the third round of a Grand Slam in 17 prior attempts.
“I knew I had the chance to beat anyone if I played my game. I am excited to be in the final and to beat Serena as she is such a great champion.
“Even when she was down a set and break she was still fighting. I had to fight hard to win.”
Pliskova saved a match point against Venus Williams in round four and becomes only the fourth woman to beat both Williams sisters in the same Grand Slam tournament.
Kerber, 28, was asked about her new-found number one status as she headed to court for the second semi-final, but insisted: “I’m just thinking about this match.”
That appeared the case as she raced into a 4-0 lead after just 16 minutes, her aggression from the baseline too much for Wozniacki, a former world number one now down at 74th in the rankings.
