Novak Djokovic didn’t want to talk about his improved left shoulder injury or the heckler whose comments helped the defending champion reach the US Open’s last 16 on Friday.

So it’s unclear exactly what medical treatments for his injury or emotional inspiration from a critic helped the world No 1 defeat 111th-ranked American Denis Kudla 6-3, 6-4, 6-2 to reach the fourth round at Flushing Meadows.

Djokovic was treated throughout his second-round match for left shoulder pain but dispatched Kudla with no outward sign of trouble.

“It’s almost pain-free. Has a little bit of pain, but I’m really pleased with the way it went,” Djokovic said. “Today the situation was much, much better than the last match, so we’ll see tomorrow.”

Djokovic, who has won four of the past five Grand Slam events and 16 overall, advanced to a fourth-round meeting with three-time Slam winner Stan Wawrinka. They haven’t played since the Swiss 23rd seed beat Djokovic in the 2016 US Open final.

Djokovic said he skipped practice on Thursday in favor of treatment on his shoulder but wouldn’t talk about how the setback took place or what he did to ease the pain.

“Forgive me, I’m not going to talk about it,” Djokovic said. “I would appreciate if you respect me not talking about it in details.

“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 a lot of things in the last few days to be able to play.”

Djokovic was captured on video having a talk with a heckler during his pre-match practice session Friday afternoon, saying, “I’ll come find you. I’ll find you after. Trust me, I’ll find you.”

Asked about the confrontation he called a “little chat”, Djokovic said he would locate the heckler, “To have a drink. I liked the guy. I’m going to buy him a drink.”

As to exactly what was said, Djokovic kept that between drinking buddies, but did say it was beneficial to his overwhelming effort in ousting Kudla.

“We’ll keep it 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.”

Djokovic even had a couple of over-the-top fans against him in the match, but those he accepted as part of the Arthur Ashe Stadium atmosphere for night matches.

“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.”