Novak Djokovic has opened up on the problems he endured with his serve despite winning through to the third round of the US Open. The Serbian was leading Laslo Djere 6-4 6-4 2-0 when an abdominal issue meant his compatriot Djere was unable to continue.

It was a record win for the 37-year-old as he became the first player in history to win 90 matches in each of the four Grand Slams.

But it was far from straightforward, with Djokovic throwing down eight double faults during the clash, with his first serve percentage down at just 47 per cent.

Pressed on the issue in his post-match press conference, Djokovic admitted: "I haven't been serving well in the first two matches here so I'm still trying to find that rhythm and tempo.

"If you don't have a good percentage of first serves in you have to work for your points, particularly against a player like Djere.

"I knew coming into the match that if I don't serve well, which was the case, then I'm going to have to really grind and work for my points a lot. And that's what I guess caused the two sets to be played over two hours."

Prior to coming off court, Djokovic had also opened up on his service struggles to Nick Kyrgios, paying his friend a compliment in the process. "It should've been his second set honestly. He was 4-2 up," said the third seed.

"I served awful. Playing without a serve, you have to grind and run. Not everyone serves like you! I guess I have to rely on my baseline game."

Djokovic will face 28th seed Alexei Popyrin of Australia in round three as his quest continues for an unprecedented 25th Grand Slam title. And despite his clear concerns, he did concede he was satisfied to have progressed again.

"I have to be happy with the win," he added. "And in important points, I managed to play one more ball over the net than him, anticipate well and find the right shots, like on set point in the second set."

And in a warning to rivals, he concluded: "The matches will only get tougher from here on in, I know that but I'm fine. I will find my way as I have done many times in my career."

Despite being in visible pain, Djere attempted to continue at the start of the third set. But after failing to win a point in the first two games, he walked to the net and shook hands with Djokovic.