A heartbroken Juan Martin del Potro said he felt "very sad for being a loser" as he graciously acknowledged Novak Djokovic was just too good in the US Open men's singles final.

Wimbledon champion Djokovic claimed his third title at Flushing Meadows - and equalled Pete Sampras' haul of 14 grand slam crowns - with a hard-fought 6-3 7-6 (7-4) 6-3 victory.

Del Potro - back in a grand slam final for the first time since he triumphed in New York nine years ago - threw everything he had at his friend and rival, but Djokovic's tremendous defensive skills and court coverage proved decisive.

Answering the first question of his news conference, Del Potro said: "To be honest, I was crying until now. I'm very sad for being a loser today."

"This is a tough loss for me. I'm really sad to lose the final. But Novak deserved to take the trophy. He played a great match, very smart game."

"I had my opportunities during the second and third set, but I was playing almost at the limit all the time, looking for winners ... and I couldn't make it because Novak was there every time. He's a great champion."

Elaborating on his increasingly attacking approach as the match wore on, Del Potro added: "It's the only way to beat these kind of players. You have to play a perfect game for more than three hours."

"Sometimes you can't make it, but my mistakes were because of the level of Novak. He played really well."

"It's really difficult to beat a player like Novak, but I did a big effort also and I'm proud of that."

Plenty of joy was derived from seeing Del Potro back in a major final after career-threatening wrist injuries robbed him of almost three full seasons following his 2009 US Open win.

Asked about his fitness, he said: "I'm feeling good. My wrist is responding good, because I've been playing a lot of matches in these two weeks."

"I feel good with my two-handed backhands as well. I'm excited to keep surprising myself doing things like this. I'm very motivated to keep trying to win these titles."