Alexander Zverev continued his search for a first Grand Slam title with victory over Alexandre Muller to reach the US Open third round.

Germany's Zverev, 27, reached the final in New York in 2020 as well as the French Open final earlier this year.

However, he lost the US Open showpiece to Dominic Thiem from two sets up, and led Carlos Alcaraz by two sets to one in Paris before succumbing to the Spaniard.

Zverev said he had doubts he could return to the top level after suffering a serious ankle injury at the French Open in 2022.

The fourth seed has won 54 singles matches this year - more than any other male player on the tour - and added another to his tally with the 6-4 7-6 (7-5) 6-1 over France's Muller.

"I had so many doubts, question marks whether I would ever be top 10 or top five in the world [again]," Zverev said.

"What changed is I'm enjoying every single moment on these beautiful courts in front of thousands of fans.

"It was something that was taken away from me two-and-a-half-years ago and I'm extremely glad to be playing at this level.

"Hopefully I can give myself the best chance to win here."

Zverev will face Argentina's Tomas Martin Etcheverry next.