It’s been five years since Kei Nishikori upset Novak Djokovic in the semifinals of the U.S. Open to secure his first, and so far only, appearance in a Grand Slam final.

At the time it was seen as a stroke of luck that Roger Federer, having been upset himself by Marin Cilic, wasn’t awaiting him in the championship match.

But Nishikori failed to take advantage, falling to an on-fire Cilic in straight sets.

Heading into the final major of 2019, which begins Monday in New York, Nishikori is no closer to achieving a breakthrough despite a level of consistency at recent Grand Slam events that can only be topped by the “Big Three” of Djokovic, Federer and Rafael Nadal.

Realistically, the 2014 U.S. Open may have been his one big chance to win a major.

“He’s outmatched is what it boils down to. There would have to be a number of things that would fall his way in order for him to make that type of run again,” seven-time Grand Slam champion John McEnroe said during a conference call with reporters Friday. “I think he’s done as well as he possibly could.”

The Japanese star’s run at Wimbledon earlier this summer is a prime example of the challenge facing a generation of players struggling to break the Big Three’s iron grip on the sport’s biggest trophies.

Nishikori raced through the first four rounds in London — atypical for a player known for marathon matches and a brilliant record in fifth sets — dropping a single set and spending less than nine hours on court.

But like a 1920s pitcher who managed to get past Earle Combs and Mark Koenig, Babe Ruth, Lou Gehrig and Bob Meusel awaited him in tennis’ version of the New York Yankees’ Murderers’ Row.

First it was Federer, the eight-time Wimbledon champion. Nishikori came out firing, punishing the Swiss star’s second serve and moving the 37-year-old around the court on his way to securing the opening set. But, as he’s done countless times in his storied career, Federer raised his level from that point forward. Ultimately, he rolled to a four-set win.

If Nishikori had managed to play the match of his life and get past Federer, Nadal would have been his opponent in the semifinals and then Djokovic in the finals. To beat all three would mean accomplishing something that no one has ever done before at a single slam.

Earlier this season, Nishikori’s Australian Open and French Open runs came to an end at the hands of Djokovic and Nadal, respectively. Last year, it was Djokovic who got the better of him both at Wimbledon and at the U.S. Open.

“I’m not sure there’s a whole lot he can do,” McEnroe said when asked to comment on Nishikori’s strategy against the Big Three. “It’s hard for him to dictate against those guys. They dictate to him. He has to react. It’s hard to do that.”

“He’s absolutely, in my book, tried everything he could to hang with these guys. I think he should be very proud of that.”

Nishikori, seeded No. 7, secured a favorable draw and will begin his 2019 U.S. Open against Marco Trungelliti. If he emerges from a section that also features Borna Coric, Milos Raonic and Alex de Minaur, then Federer, Djokovic and Nadal, in that order, could be in his path to the title.

“He’s got a fairly good-looking draw that could allow him to make a run to the quarters, then you never know. You just got to hope things fall your way,” McEnroe said.