Seeking that record-breaking 25th grand-slam triumph that feels increasingly elusive, the great Djokovic found himself stuttering on Arthur Ashe Stadium on Wednesday after spraying around 14 unforced errors while losing the first set of his second-round clash to American qualifier Zachary Svajda.
Like his laboured first-round win over Learner Tien, the 38-year-old looked occasionally out-of-sorts and a bit rusty again before he finally found some rhythm and made only 11 more mistakes en route to beating the world No.145 Svajda 6-7 (5-7) 6-3 6-3 6-1.
His path was certainly eased when the 22-year-old from San Diego seemed to be afflicted by a leg injury midway through the contest, needing physio treatment after the second set and again during the third set when his level began to dip.
Djokovic admitted he had played some discordant notes. "Wasn't happy about my tennis the first part of the match ... I didn't feel that great to be honest," he shrugged afterwards.
"It was unfortunate that he struggled with injury towards the end of the second set, but kudos to him for staying on the court. It was obvious he couldn't serve as well as he did for a set-and-a-half."
Djokovic, who made it 19 wins out of 19 second-round matches at Flushing Meadows, next plays British left-hander Cam Norrie, hoping to avoid his fate of last year when he got knocked out by Australian Alexei Popyrin in his joint-earliest exit at the US Open.
Norrie, a Wimbledon semi-finalist, got past Francisco Comesana of Argentina 7-6 (7-5) 6-3 6-7 (0-7) 7-6 (7-4) in four hours to set up his clash against Djokovic, who has a 6-0 lead in their head-to-head battles.
Asked if he feels he can play himself into form, Djokovic said: "That's what I'm hoping, that was the case for most of my grand slam career. The deeper I go in the tournament, the better I feel about my game."
Meanwhile, fifth seed Jack Draper has been forced to pull out of the tournament with injury.
Before his second round meeting with Zizou Bergs, the British hope reported the serving-arm injury which had hampered him for several weeks had become too debilitating.
Draper had struggled to beat Argentine qualifier Federico Agustin Gomez on Monday while dealing with the left-arm issue which had sidelined him since his early exit at Wimbledon last month.
"Hi guys, I'm sorry to say I'll be withdrawing from the US Open," Draper said on social media.
"I tried my very best to be here and give myself every chance to play, but the discomfort in my arm has become too much and I have to do what is right and look after myself. Thank you for all the support."
It's a blow for the rising 23-year-old, who reached the semi-finals of last year's US Open before losing to eventual winner Jannik Sinner.
It's only a matter of time before Brazilian teenage star Joao Fonseca enjoys a big grand slam breakthrough, but he'll have to wait for his moment after losing to Czech 21st seed Tomas Machac 7-6 (7-4) 6-2 6-3.
Casper Ruud, whose 0-3 record in grand slam finals includes a loss to Carlos Alcaraz at Flushing Meadows in 2022, was eliminated 6-4 3-6 3-6 6-4 7-5 by Raphael Collignon.
The 107th-ranked Belgian had never won a match at a major or played a five-setter until this tournament.
- with Agencies
