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

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

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

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

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 2004-06, and knew he’d figure things out across seven matches on the hard courts in a city where he is so comfortable.

“For a long period I think 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, all conditions, wind, you know, night, day. I really embraced everything about New York.”

Still does, which is why — at age 37, and a full decade removed from his last title at the place — Federer believes he can succeed again at the 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.

“Well, I mean, it would mean the world to me,” he 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 he could handle Federer at the U.S. Open when he stopped him last year in the quarterfinals.

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

“If you are playing well before, is easier to play well in the Grand Slam, no? No doubt of that,” Nadal said.