She was beaten in straight sets to Czech Karolina Pliskova
World number one Serena Williams has fallen short in her bid to reclaim her US Open crown after losing in straight sets to Karolina Pliskova.
The Czech number 10 seed beat her American counterpart 6-2, 7-6 (7/5) and the result dislodges Williams as world number one, after 186 weeks at the summit.
She is replaced by Angelique Kerber at the top spot, after the German beat Dane Caroline Wozniacki 6-4, 6-3 to set up the decider with the 24-year-old.
Pliskova will take her spot in a first ever Grand Slam final and looks to edge the reigning Australian Open champion.
"I was pretty calm today," Pliskova told The Guardian. "Before the match I felt a little bit like pressure, a bit nervous. But when I stepped on the court I didn’t feel anything. I just, you know, wanted to win, actually. Not just enjoy but to win."
Williams, meanwhile, refused to blame fatigue on her defeat to the Czech.
"We play every single week," she said. "I have been in Toronto or Montreal or Cincinnati where I play Wednesday, Thursday, Friday, Saturday, Sunday.
"I mean, if I’m not used to playing this, and I really should think of something different. I’m not going to sit here and make an excuse, because that’s not me.
"I’m a professional player. Been playing for over 20 years. If I can’t turn around after 24 hours and play again then I shouldn’t be on tour."
Victory in the US Open would have been a record 23rd Grand Slam title for Williams.