Novak Djokovic will replace young rival Carlos Alcaraz as the men's world number one after a routine win on his US Open return.

Serbia's Djokovic, who lost the Wimbledon final to Alcaraz, won 6-0 6-2 6-3 against France's Alexandre Muller in Monday's night session in New York.

Djokovic, 36, was not allowed to play in the United States last year because he was not vaccinated against Covid-19.

He has returned knowing another title will be a record-equaling 24th major.

Matching Australian Margaret Court's all-time tally is Djokovic's target, and he made a statement start by breezing past 84th-ranked Muller.

"I started tremendously well; we started quite late, but I was excited to go out on the court - it has been a couple of years," said Djokovic, who will spend a record-extending 390th week at the top of the ATP rankings.

"In the second and third sets, I dropped the level of my serve and had to work for the points a bit more. Nevertheless, I played great, and I liked the level."

Having started at 23:00 local time, the three-time US Open champion showed he did not want to hang around and only dropped eight points in a 23-minute opening set.

A smiling Muller raised both arms in celebration when he finally got on the scoreboard for 2-1 in the second set, but the 26-year-old could not stop Djokovic from moving further ahead.

Muller offered more resistance in the third set before Djokovic won the final four games to wrap up victory in one hour and 34 minutes.