Garbine Muguruza will become the WTA's world number one for the first time on Monday after top seed Karolina Pliskova was dumped out of the US Open at the quarter-finals by Coco Vandeweghe.
The top seed at Flushing Meadows and last year's runner-up, Pliskova needed to reach the final of the year's final grand slam to retain pole position in the rankings.
However, the Czech was overpowered by Vandeweghe, whose 7-6 (7-4) 6-3 victory keeps alive the possibility of an all-American last four in the women's singles. Sloane Stephens and Venus Williams will meet in one semi-final, while Vandeweghe now awaits the winner of Wednesday's match between compatriot Madison Keys and Kaia Kanepi.
Although Vandeweghe's performances at regular WTA Tour events in 2017 have been largely underwhelming, she has frequently impressed on the biggest stages.
A semi-finalist at the Australian Open in January, she also reached the last eight at Wimbledon this year and has now equalled her best performance at a slam.