Ash Barty suffered a surprise defeat at the hands of American Shelby Rogers losing 6-2, 1-6, 7-6 (7-5) in the US Open third round on Sunday (AEST).
Rogers, currently ranked 43 in the world, started the match in fine form with an early break seeing her wrap up the first set 6-2 to set the scene for a potential upset.
Australia's world number one battled back strongly in the second set however as she pushed the third-round match into a deciding set.
Barty started the third set with a decisive break but was broken herself twice as she looked to serve out the match.
Shelby was refusing to roll over and forced the match to a tie-break where she held her nerve to claim a tight win.
Believe it, Shelby!
— US Open Tennis (@usopen) September 5, 2021
Shelby Rogers upsets No. 1 Ash Barty in a thrilling comeback in Ashe! #USOpen pic.twitter.com/bPkjsAfNlO
An 18-year-old sensation in the form of Emma Raducanu now awaits Shelby in a fourth-round clash early next week with the qualifier looking to continue her own impressive US Open run.
Barty has never won a US Open title in singles with her best performance at the competition to date seeing her make the fourth round in 2018 and 2019.
The 25-year-old has however had doubles' success in the tournament and won the title with CoCo Vandeweghe in 2018.
Barty claimed her first Wimbledon title in July this year and also picked up a bronze medal in mixed doubles at the recent Tokyo Olympics.
The Australian revealed in July that her Wimbledon success was all the more special considering the odds of her being fit in time for the tournament.
"They kept a lot of cards close to their chest and didn't tell me a lot of the odds, didn't tell me a lot of the information that they'd got from other specialists," Barty said.
"I think them not telling me that just proved how much we were up against the odds. There weren't too many radiologists in Australia who had seen my injury. In a sense, it was a two-month injury.
"Being able to play here at Wimbledon was nothing short of a miracle.
"I think now to be playing pain-free through this event was incredible. Certainly now chatting to them it looked a lot less likely than I felt statistically. I think it's been an incredible month."