New York - Roger Federer feels as strong as he has "in years" entering the US Open, having put behind him an epic loss to Novak Djokovic in last month's Wimbledon final.

"This is probably the best I've felt in years coming into the US Open again, which is encouraging," Federer said.

"I'm ready for the US Open. It's going to be a tough tournament to win, no doubt about it. I feel like I'm part of that group who can do it."

The 38-year-old Swiss star owns a record 20 Grand Slam singles titles but squandered two championship points in the fifth set and fell 7-6 (7/5), 1-6, 7-6 (7/4), 4-6, 13-12 (7/3) after four hours and 57 minutes - the longest singles final in Wimbledon history.

There's still a sting for Federer to be the first player since 1948 to lose the Wimbledon men's final after being one point from victory. But he is hoping to channel the emotions positively at the US Open.

"I've been there before, had some tough losses along the way. So many great wins, as well," Federer said.

"I was just more upset rather than being sad. I think being upset made me get over that finals much easier than being sad, dwelling over it too much. I was not going to be too down on myself.

"I hope it's obviously going to help me for here."

Third-seeded Federer opens on Monday night at Arthur Ashe Stadium against 190th-ranked qualifier Sumit Nagal of India.

Federer admitted struggling for a couple of days after the Wimbledon final loss but a caravan vacation with his wife and four children left little time for regrets.

"I didn't have that much time thinking about all the missed opportunities," he said.

"Sometimes you have flashbacks - I could have done that, should have done that. Next day you're having a glass of wine with your wife thinking, 'The semis was pretty good. Even the finals was pretty good'."

Federer arrived in New York off his fastest loss in 16 years, falling to Andrey Rublev in the Cincinnati third round in only 62 minutes.

"Cincinnati might be a good thing that I lost early. Who knows?" said Federer.

"It's maybe one of those things that sometimes needs to happen, like when I won at the Australian Open, went to Dubai, lost first round in '17, then went on to win Indian Wells and Miami.

"Played a great Wimbledon. Needed to get knocked down in Cincy, get my act together, train hard. That's what I did."

Since losing to Juan Martin del Potro in the US Open final a decade ago to snap his run of five consecutive titles, Federer has reached the Flushing Meadows final only once, falling to Novak Djokovic in 2015.

Federer lost in last year's fourth round to Australia's John Millman.

"It hasn't always been easy here," Federer said.

"Two years ago I came in with a back issue a little bit, I had a struggle early on with five-setters. That set the tone the tournament was going to be tough.

"Last year I struggled with the heat against Millman. Obviously, what was it, '16 I missed it entirely.

"I have no explanation why it didn't go as well as it did. I think a bit unlucky for sure also. That was part of it, yeah. More health unlucky."

Federer isn't adding to the pressure already upon him as the all-time men's record Slam singles champion.

"I'm not putting extra pressure on myself. I know it's going to be tough," he said.

"What I'm very proud of is I've had a very consistent last year and a half.

"I've been playing well in Slams recently, which has been great. I think also the win over Rafa in the (Wimbledon) semis was big for me. Also the finals, the way I played that in Wimbledon, is going to give me some extra confidence."