Serena Williams' 186-week reign as world number one is over as Karolina Pliskova beat her 6-2 7-6 (7-5) in the semi-finals of the US Open.
Pliskova - who had never been beyond the third round of a grand slam before this tournament - dominated the first set, breaking Williams twice and holding all of her games with a strong serve.
But the second set was a lot closer. The 10th seeded Czech broke Williams in the fifth game, only for the top seed to immediately break back with a phenomenal game that kept Pliskova unable to score once off her own serve.
But it was Pliskova who managed to hold her nerve in the tiebreak, winning it 7-5.
Williams, whose 22 grand slam titles has her tied with Steffi Graf, was bidding to break the professional era record with victory in New York.
It was the second consecutive year she lost in the US Open semi-finals while chasing history - last year she was attempting a rare calendar-year grand slam, but was upset by Roberta Vinci.
Williams had to back up from her three-set quarter-final win against Romania's Simona Halep yesterday, and has to call the trainer out during today's match to work on her leg.
But she denied that fatigue had nothing to do with the loss.
"I've been having some serious left knee problems but I wasn't tired, fatigue had absolutely nothing to do with it I mean, if I was tired I should definitely get into a new career," Williams said.
"I wasn't able to move the way I wanted to move or...when you're injured you're thinking of other things when you should be just playing and thinking up your shots and my line was just a little bit everywhere.
"I was making errors that I never make and definitely I didn't make in this tournament in particular.
"So many simple, simple shots that I easily could've made and I just blame that on mentally thinking about my leg and just not thinking about the shot."
Karolina Pliskova, who had earlier knocked the sixth-seeded Venus Williams out of the tournament, said she was thrilled with her effort.
"I mean, there is not more than to beat both sisters in one tournament in New York," she said.
"For the crowd, it's not probably the best that I beat both of them in their country, but for me it's really something special.
"Once I beat Venus here I knew I'm playing good tennis and I have a chance to beat anyone in the tournament.
"Serena, she's a champion so it's never easy to play her. You saw even when she was down a break she's still fighting so it's very hard.
"I was expecting tough match but I knew I can win."
The 10th-seeded Czech moves into the final at Flushing Meadows to meet Germany's Angelique Kerber, who will replace Williams as the world's top-ranker player on Monday no matter what the result.
- RNZ, Reuters