Daniil Medvedev recovered from a mini meltdown to beat Australia's Christopher O'Connell 6-2, 6-2, 6-7 (6/8), 6-2 and reach the US Open third round.
The third seed and 2021 champion looked to be cruising into the last 32 in New York for the seventh year running after moving a break up in the third set against his 69th-ranked opponent.
But O'Connell hit back and then saved two match points in the tie-break as Medvedev grew increasingly rattled, the Russian double-faulting twice to send the contest to a fourth set.
In a sign of Medvedev's fraying nerves he called the doctor out after the third set, sarcastically replying "Yeah, I lost the set" when asked if he was experiencing any symptoms.
Medvedev regrouped and surged 4-1 ahead, saving three break points in the seventh game as O'Connell received treatment to his knee, before finally sealing victory past 1am local time Friday.
"Tough match. I don't know why but one moment in the match he decided to play much better. I don't know why was the reason, but it became much tougher for me," said Medvedev.
"I had opportunities in the third (set) and I managed to use them in the fourth.
"You kind of don't know when you get frustrated, you never know you could be. I felt today maybe it helped me a little bit."
He next plays Argentina's Sebastian Baez, the world number 32 and winner of 12 matches in a row following his titles at Kitzbuehel and Winston-Salem.
mw/rcw
