The reigning champion and number one seed Naomi Osaka has been beaten in straight sets in the US Open round of 16 by Swiss star Belinda Bencic.
The 21-year-old, who saw off 15-year-old Coco Gauff in the last round, was beaten 7-5, 6-4 at Arthur Ashe Stadium.
The result means the Japanese star will lose her world number one ranking - with Australian Ashleigh Barty set to take the spot.
Barty won the French Open earlier this year at Roland Garros. She was knocked out in the last 16 by China's Qiang Wang at Flushing Meadows on Sunday.
Defending champion dethroned @BelindaBencic shocks Naomi Osaka and scores her third win of the year over the world No. 1.
Match report ➡ https://t.co/CBlmr7ItTo pic.twitter.com/2gwFFLXhPG— US Open Tennis (@usopen) September 2, 2019
Osaka won the US Open last year by beating Serena Williams in the final, and after her Australian Open triumph at the beginning of this year became the top-ranked player in the women's game. She was replaced by Barty in June.
It will be a second quarter-final appearance at Flushing Meadows for 22-year-old Bencic. She also made the last eight in 2014 and is now set to take on one of 23rd seed Donna Vekic of Croatia or Germany's Julia Goerges, the 26th seed.
Bencic has a good record against big-time competition - the number 13 seed has had more victories over Top-10 competition than any other player this year. This is the third time this year she has beaten Osaka. One of those wins came at the Indian Wells tournament in March.
Bencic broke Osaka at 5-5 in the opening set with two terrific points with the game locked at 30-30.
Bencic held serve for the first set, in which she won 73 percent of her first-service points. Osaka only notched one break point in the entire set.
The result means the top seeds are now out of both the men's and women's draw at the tournament - and both were knocked out by Swiss opposition.
Novak Djokovic had to retire with a shoulder injury during his match against Stan Wawrinka. Djokovic had trailed by two sets and had just gone a break down in the third when he called an end to his participation in the match.
Second seed Rafael Nadal takes on Croatian Marin Čilić from around midnight tonight Irish time in his round of 16 tie.
