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 willface Angelique Kerber or Carolina Wozniacki in the final.
The result guarantees that Germany’s 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 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.”