Japanese teenager Naomi Osaka admitted she had "freaked out" as her big lead slipped away against Madison Keys at the US Open.
Osaka was reduced to tears as American eighth seed Keys claimed a dramatic 7-5 4-6 7-6 (7-3) comeback win to reach the fourth round.
Leading 5-1 in the third set and on the cusp of the biggest victory of her career, Osaka crumbled as Keys swept the next five games en route to a victory that stunned her 18-year-old opponent.
"Those aren't the most fun matches but I just knew that if I stayed in the match that I could maybe have a chance to come back and get back in it," said Keys, who will next meet former world No.1 and US Open finalist Caroline Wozniacki.
"Once I was able to get a little bit of momentum, I felt like I found my game a bit more. At that point, I knew I had to kind of step up or else I was going to be going home."
The excruciating collapse by Osaka played out on one of the game's biggest stages.
The Japanese world No.81 was in tears several times, a distraught Osaka at one point hanging her head and covering her eyes as she walked to a corner of the court.
But there was no place to hide inside the massive Arthur Ashe Stadium from the gaze of thousands of fans or a ruthless Keys, who moved in for the kill and clinched the comeback when Osaka sent a return wide.
Osaka's meltdown was in many ways reminiscent of a distraught Martina Hingis collapse to Steffi Graf on centre court at Roland Garros in 1999 and Jana Novotna's tearful loss to Graf in the 1993 Wimbledon final when the Czech sobbed on the shoulder of the Duchess of Kent.
Meanwhile, Britain's Johanna Konta looked back to full fitness as she swept past Switzerland's Belinda Bencic 6-2 6-1 to reach the last 16.
A semi-finalist at the 2016 Australian Open, the Sydney-born 13th seed Konta never allowed Bencic into the match, hitting eight aces as she matched her best effort in the season's final grand slam at Flushing Meadows.
Wozniacki continued her resurgence with a commanding 6-3 6-1 win over Romania's Monica Niculescu.
The Dane, a US Open finalist in 2009 and 2014 but unseeded this year after being sidelined for two months by an ankle injury, dominated from the start and wrapped up victory in just under an hour-and-a-half.
Niculescu, ranked 16 places above Wozniacki in the rankings at 58th, made life tough early on, particularly with her sliced forehand which is a rarity on the WTA Tour.
And Angelique Kerber, enjoying a breakout season that has her challenging for the world No.1 ranking, crushed 17-year-old American qualifier CiCi Bellis 6-1 6-1 to reach the fourth round.
Next up for Kerber is Petra Kvitova of the Czech Republic, a 6-3 6-4 winner over 22nd seed Elina Svitolina of Ukraine. Kerber and Kvitova have split their eight career meetings.