NEW YORK — Even with all the times Roger Federer has held the U.S. Open trophy, he still can’t forget the time it slipped through his fingers.

He had won five consecutive titles in Flushing Meadows and was a game away from a sixth in 2009 when Juan Martin del Potro pulled out a fourth-set tiebreaker and then won the fifth set.

“I still wish I could have played that match again,” Federer said Friday.

He never has been that close to winning the U.S. Open since, reaching the final just once.

That would have been hard to imagine then, when Federer would steamroll into New York at the tail end of some of the greatest seasons in tennis history. He was 247-15 from 2004 to 2006 and knew he would figure things out across seven matches on the hard courts in a city where he is so comfortable.

“For a long period I was not losing much,” Federer said, “and when I came to the Open I had all the answers for all the guys, all my opponents [and] all conditions — wind, night, day. I really embraced everything about New York.”

He still does, which is why — at 37 and a full decade removed from his last title here — Federer believes he can succeed again at the year’s final Grand Slam tournament and collect a male-record 21st major when main-draw play begins Monday. A sixth U.S. Open title would break a tie with Jimmy Connors and Pete Sampras for the most in the professional era.

“It would mean the world to me,” Federer said.

Novak Djokovic just beat Federer in the final in Cincinnati, and the Wimbledon champion might be the favorite in New York. Defending champion Rafael Nadal is the top seed after taking back the No. 1 ranking that Federer had regained earlier this season for the first time in five years, and del Potro is up to a career-best No. 3 in the world and proved again last year that he could handle Federer at the U.S. Open when he stopped him in the quarterfinals.

Yet few would count out No. 2 seed Federer, even as erratic as his gifted game looked against Djokovic last weekend in Ohio.

“If you are playing well before, [it’s] easier to play well in the Grand Slam,” Nadal said. “No doubt of that. At the same time it’s true a few players are able to increase the level of concentration, level of tennis, level of intensity in some places. If you have to do it, this is one of the places.”

Federer hasn’t done it in the biggest moments over the last decade.

The 2009 loss to del Potro was followed by semifinal defeats against Djokovic in 2010 and 2011, when Federer blew two match points in both. He finally got back to the final in 2015 but was beaten by Djokovic. He missed the 2016 tournament because of a knee injury.

Federer won the Australian Open and Wimbledon in a resurgent 2017, but he tweaked his back while reaching the Montreal final and knew his body and game weren’t in shape by the time he got to New York.

“I knew from the get-go it was not going to be possible for me to win,” Federer said. “Everything would have had to fall into place.”

So he was even more cautious in monitoring his schedule this year, sitting out the clay-court season again and pulling out of Toronto, making Cincinnati his only hard-court warmup. That has left Federer with only four tournaments in five months and perhaps explains some of the shots that once were winners but were sprayed around the court against Djokovic.

Federer won’t second-guess his scheduling, believing he has made the right decisions for his preparation. Nor will he kick himself over the U.S. Opens lost over the last decade.

“I won the U.S. Open five times, so I stand here pretty happy,” Federer said. It’s not like, ‘God, the U.S. Open never worked out for me.’ It hasn’t the last couple years, but it’s all good.”