NEW YORK -- Defending champion Novak Djokovic said a prematch spat with a fan during practice inspired him, as he raced past Denis Kudla 6-3, 6-4, 6-2 to reach the fourth round of the US Open on Friday.
The world No. 1 was captured on camera having a heated discussion with someone through the fence at the back of the practice courts, saying: "I'll come find you. I'll come find you afterwards, trust me, I'll come find you."
Djokovic would not go into details as to what sparked the row but said they "just had a little chat" and that he wanted to find him "to have a drink. I liked the guy. I'm going to buy him a drink."
"We'll keep [what he said] between us. ... But he definitely helped me. He doesn't even know, but he did help me," Djokovic said. "I'm not going to talk about it. I think he did me a favor. Even maybe he didn't want to do me a favor, he did me a favor, big favor."
The three-time champion also had a number of interactions with the crowd inside Arthur Ashe Stadium in what was a typically rowdy US Open night session.
In the first set, when one fan yelled out in the middle of a point, an angry Djokovic shouted: "Shut the f--- up."
Later in the match, he took issue with two fans dressed in bathrobes -- one wearing a shower cap and the other a football helmet -- one of whom cheered when he double-faulted.
Djokovic said the incident had fired him up.
"Yeah, I was. Night sessions, New York, crowd gets into it," he said. "A couple guys that had a couple of drinks more than I guess they were supposed to. But it was all good after."
Djokovic had been scheduled to practice at 5 p.m. ET, but he moved it to 6 p.m. and then 7 p.m., prompting fears that the left shoulder injury that had bothered him in his previous round might prevent him from playing against Kudla.
He eventually came on to court just before 7:45 p.m., and after a gentle practice, he headed for the match court, where he showed no signs of discomfort with the shoulder.
"It's almost pain-free," he said. "Has a little bit of pain, but I'm really pleased with the way it went."
Asked if he'd had a pain-killing injection, Djokovic would not say.
"I would appreciate if you respect me not talking about it in details," he said. "I mean, I understand you guys want to know. I made a decision not to get into details, not to speak about it. Please understand me.
"I'm very glad with the way it went. I am able to play. That for me is a huge blessing today because it was probably the complete opposite two days ago.
"I did not practice yesterday, that's true. I did a lot of things in the last few days to be able to play."
Djokovic will play former US Open champion Stanislas Wawrinka in the fourth round.