Six games, that's all Novak Djokovic released against Damir Dzumhur in his first match at this year's US Open.

In front of the empty stands at Arthur Ashe Stadium in Queens, New York, Djokovic broke the Bosnian serve for the seventh time in the match, winning 6-1, 6-4, 6-1.

Behind the clear victory figures hides a lot of frustration on the part of the world set, and it was clear early on that it was only his own mood and thoughts that could disturb the world set's path towards the second round.

Undefeated this year

- I think I started well, with a set and a serve breakthrough up.

But then it became a little more complicated, he says in the victory interview.

- I lost focus, he started to miss a little less and got a good variation on his strokes and there, in the middle of the match, I thought it could go anyway.

But Dzumhur could not resist the hard-serving Serb, and accounted for more and more errors in the third set.

Djokovic, who on Sunday took his fourth title of the year, has thus not yet lost a competitive match on the ATP Tour this year.

On his way to the title at the Cincinnati Masters, which this year moved from Ohio to New York, he needed treatment for his neck and question marks over his physical status have been raised.

- I feel good.

Honestly, I fought a lot in the semifinals and the final, but I have had two days to catch up, says Djokovic, who next has to take on the British Kyle Edmund on his way to a haunting 18th grand slam title and the fourth in New York.

Most of the highly ranked men's players in the tournament advanced from the first round.

Fourth-seeded Greek Stefanos Tsitsipas dropped just four games against Spaniard Albert Ramos-Vinolas, while German Alexander Zverev, ranked fifth, needed four sets to defeat South African Kevin Anderson, who was in the final in New York three years ago.

The Argentine Diego Schwartzman, thus became the highest seeded male player to go out during the first day of the tournament.

Ninth-seeded Schwartzman fell in five sets against British Cameron Norrie.