Daria Kasatkina has overcome painful cramping and a dogged opponent to avoid the Australian exodus on day five at the US Open in New York.
Kasatkina battled back from a break down in the deciding set to live up to her 15th seeding and deny her friend and former compatriot Kamilla Rakhimova in a two-hour, 22-minute epic at Flushing Meadows.
As Alexei Popyrin, Adam Walton and Tristan Schoolkate all crashed out, Kasatkina expressed pure relief at joining Australian qualifier Priscilla Hon in the last 32 with a fighting 6-2, 4-6, 7-5 comeback victory.
"When I was 4-1 down, I was just like, 'Oh my God'. I I also started cramping," the world number 18 said.
"I don't know actually how I was able to come back and win.
"My finger was cramping. My quad was cramping. I was just running on the court trying to finish as quickly as possible.
"I'm really happy with my effort today because even though I was not playing my best tennis, I was still able to get this win."
Earlier, Popyrin proved no match for the defending US Open champion Jannik Sinner, who effortlessly brushed aside the Australian 6-3, 6-2, 6-2 to advance to the third round.
The metronomic world number one, looking to become the first man to retain the trophy at Flushing Meadows since Roger Federer won the last of his five crowns in 2008, was expected to face a tricky test against a tenacious opponent on Thursday, local time.
"Obviously, I try to play the best tennis I can," said Sinner, who plays Canadian 27th seed Denis Shapovalov in the next round.
"The first round matches are always different compared to the further you go (in the tournament). I'm very happy that I managed these matches as good as I could, when you are up two sets and a break, you try to serve as best as you can.
"Today it felt like neither of us served well, but I was returning well, especially on the second serve. I'm happy about today. I'm aiming to improve on the serve but the rest (of my game), I'm quite comfortable with."
But Popyrin, who arrived at Arthur Ashe Stadium hoping to knock out the holder for a second successive year after toppling Novak Djokovic 12 months ago, landed in a world of trouble early on when Sinner forged a 4-1 lead with a reflexive return.
Sinner wrapped up the opening set on serve and then had the bandages on his right foot trimmed by a physio during the break, before the 24-year-old promptly resumed his mission to scythe down his 36th-ranked opponent in the second set.
The top seed forced an error from Popyrin's racquet for an early break, and although he faced some resistance while serving in the sixth game, comfortably took the second frame by trading his powerful hitting for a soft drop at the net on set point.
Popyrin's win over Sinner in their only previous meeting at the 2021 Madrid Open began to look increasingly irrelevant when he fell behind in the third, before his opponent put him out of his misery with a thunderous ace.
The usually understated Sinner, who is aiming to go level on five Grand Slam trophies with his charismatic title rival Carlos Alcaraz, will now have a day to recover and said he had a number of Italian restaurants in mind to indulge his appetite.
There was good news late in the evening, as Alex de Minaur hit the go button in a straight-sets victory over Japanese qualifier Shintaro Mochizuki.
The world number eight did not have it all his own way, de Minaur staving off 11 break points in the opening set before seizing control for a 6-2, 6-4, 6-2 victory on showcourt Stadium 17.
However, Maya Joint's tournament ended with a 7-6 (7/2), 6-2 loss to American Amanda Anisimova on Louis Armstrong Stadium.
AAP/Reuters/ABC
