World number one Novak Djokovic insisted he was not acting like a "spoiled brat" after complaining about a noisy spectator during his routine second-round win over Tallon Griekspoor at the US Open.

The Serbian's quest for a calendar grand slam rarely looked like being derailed after posting a 6-2 6-3 6-2 win over the Dutchman on Arthur Ashe Stadium, even if a fan tried his best.

A rowdy spectator sat courtside was intent on trying to put Djokovic off, shouting right before he attempted an overhead smash, which was subsequently missed.

He continued to call out at key moments, which led the 20-time grand slam champion to complain to the umpire.

But Djokovic said: "When tennis players talk about that, someone who is watching team sports would say, 'What a spoiled brat'.

"But it's a different sport. Look, there's a lot of noise happening on the stadium, particularly in the night sessions. I don't mind that.

"Even sometimes during the point it happens that people out of excitement, they just scream or they release like a sound or whatever, sigh, whatever you call it. And that's fine.

"But if someone intentionally does it over and over again, then I have tolerance up to a certain point, then it's not correct, then it's not fine. It's not fair. I feel like it's not good for us players.

"I mean, particularly that guy for some reason was calling, raising the sound and kind of screaming just before I would hit my smash, which was a big point. Before that he would do a few times. After that again.

"That wasn't nice. That's all. I don't mind the noise. Don't get me wrong. I think it's important for the entertainment, for the crowds, the music.

"I get it. But if someone does it over and over again, particularly when you are at his side, he knows why he's doing it.

"The guy that I pointed out, he knew exactly what he was doing, and that's all."

Djokovic is aiming to add the US Open to his 2021 collection of Australian Open, French Open and Wimbledon titles and will next face Kei Nishikori.

The German reached his first slam final at Flushing Meadows last year and led Dominic Thiem by two sets to love before the Austrian somehow found a way back.

"It was painful," said Zverev. "I still remember it every single time I walk on this court but I take it as motivation because I'm back here, I have the opportunity to do better, I have the opportunity to hopefully play a great tournament, hopefully play for a grand slam title."

Wimbledon runner-up Matteo Berrettini did not have things all his own way against Frenchman Corentin Moutet but came through 7-6 (2) 4-6 6-4 6-3 while 22nd seed Reilly Opelka was a 7-6 (1) 7-5 6-4 winner over young Italian Lorenzo Musetti.

There was a shock on Court Five, where veteran Italian Andreas Seppi, playing in an 18th consecutive US Open, defeated 10th seed Hubert Hurkacz 2-6 6-4 6-4 7-6 (6).

Seventh seed Denis Shapovalov made light work of Spaniard Roberto Carballes Baena, winning 7-6 (5) 6-3 6-0.