Jannik Sinner is proud of his "incredible year" but is still targeting improvements despite picking up his second grand slam win at the US Open.

The Italian edged a tight contest in straight sets, claiming his maiden title at Flushing Meadows with a 6-3 6-4 7-5 victory over home favourite Taylor Fritz on Sunday.

In the process, the world number one became just the third player to win the title at the US Open men's singles after dropping his opening set at the event in the past five decades, after John McEnroe (1981) and Patrick Rafter (1998).

Sinner fell behind in the final set and had to dig deep to overcome Fritz's late fight, and said that his self-belief ultimately carried him over the line.

"I just went day by day. Believing in yourself is the most important," Sinner said in his on-court interview.

"I understood, especially in this tournament, how important the mental part is in sport.

"It's been an incredible year. So many big wins, starting off in Australia which gave me confidence until now.

"The work never stops. I know I can still improve. I can't wait for my continued process.

"I love tennis. I practice a lot for this kind of stage. I know how much work Taylor puts in. He's doing an amazing job and congrats to you and the whole team.

"It's so nice to see you on big stages like this, and I'm quite sure there will be many more. I wish you the best of luck for the future."

Just before the start of the US Open, Sinner was cleared following an investigation, having twice tested positive for a banned substance in March.

The 23-year-old was inadvertently contaminated by a low level of a metabolite of clostebol – a steroid that can be used to build muscle mass – by his physiotherapist, who had used an over-the-counter spray for a cut on his own hand before treating the player.

With many worried about how that would affect Sinner's focus in New York, he credited his team for helping him get through the tough period.

"This title for me means so much because the last period of my career was really not easy," Sinner added.

"My team and the people who are close to me have supported me every day. I'm very happy and proud to share this moment with my team."