Novak Djokovic kisses the trophy after defeating Juan Martin del Potro in the U.S. Open final for his second Grand Slam title this year. (Adam Hunger/AP)

Novak Djokovic authored a reminder Sunday at the U.S. Open: When it comes to Grand Slam tennis, he is not going anywhere.

After a 2017 season in which Roger Federer and Rafael Nadal ushered in a new age for men’s tennis in which knee injuries, elbow injuries, wrist injuries and age are mere detours — not downfalls — for the sport’s greats, Djokovic has proved he belongs twice over. He closed the 2018 Grand Slam season with a win over Juan Martin del Potro to claim his third U.S. Open title on the heels of his recent triumph at Wimbledon.

He sealed the 6-3, 7-6 (7-4), 6-3 victory with a forehand winner before he crumpled to the court at Billie Jean King National Tennis Center.

The win means plenty for Djokovic, 31, in tennis’s current age. It was his 14th Grand Slam title, which ties him with his childhood hero Pete Sampras for third on the all-time major singles titles list behind Federer’s 20 and Nadal’s 17.

“The first actually thing I saw related to tennis on the TV was his first or second Wimbledon championship,” Djokovic said of Sampras. “That inspired me to start playing tennis. There is a lot of significance of me being now shoulder to shoulder in terms of Grand Slam wins with him. It’s truly incredible when you think about it. . . . I grew up playing and thinking that one day I’ll be able to do what he does. To actually be here, it’s a dream come true.”

The No. 6 seed won a knotty, loud but drama-free final as the tennis world was still reeling from Saturday’s controversial women’s title match between Serena Williams and Naomi Osaka, and he won with the crowd clearly against him.

His victory follows a Wimbledon title that announced his return to the game’s top tier after a February surgery waylaid him for a few months. The U.S. Open championship took his resurgence a step further.

“If you told me in February this year when I got the surgery that I’ll win Wimbledon, U.S. Open and Cincinnati, would be hard to believe,” Djokovic said. “But at the same time, there was always part of me that imagined and believed and hoped that I can get back on the desired level of tennis very soon.”

Many predicted top-seeded Nadal would be the one most capable of surviving the intensely hot, humid conditions and night matches that stretch into the early-morning hours at the year’s final Grand Slam.

But the Spaniard retired in the semifinals when his troublesome right knee gave way to what the world No. 1 said was a flare-up of preexisting tendinitis. Federer, the No. 2 seed and another favorite here, lost in the fourth round.

That left Djokovic, who missed the U.S. Open last year because of a right elbow injury, as the last man standing to defend the title streak of the “Big Four” against a man who had broken it once before.

Del Potro won the only Grand Slam title of his career by upsetting Federer in New York in 2009 but couldn’t swing the upset Sunday. Djokovic, Federer, Nadal and Andy Murray have now won 50 of the past 55 Grand Slams.

Stan Wawrinka (three), Marin Cilic and del Potro captured the other five.

“We are proud to be close to these legends,” said del Potro, 29. “I’ve spent all my career learning with Novak, Roger, Rafa, seeing them winning these events very often. It’s amazing. I don’t feel sad that I couldn’t win Grand Slams because of them. I am just one of the guys that is lucky to be in the same era as them.”

The Argentine put his admiration aside Sunday and made it hard for Djokovic to gain an edge.

The match’s turning point came in the eighth game of the second set, after Djokovic had lost three straight games and was trailing 3-4 on serve.

He had grown frustrated by the pro-del Potro crowd that sang and chanted his name throughout the 3-hour 16-minute match as if it were a soccer game. The most common utterance from chair umpire Alison Hughes aside from the score was undoubtedly, “Quiet please, players are ready,” as she tried to stifle the rowdy spectators so del Potro and Djokovic could serve. It was even louder because of the closed roof over Arthur Ashe Stadium to keep out the rain.

Djokovic glared at the crowd and tossed his hands up in disbelief after losing one 16-shot rally, then he steadied himself and fended off three game points that would have given del Potro a two-game lead in the set.

Eventually, the Serb held. The game lasted so long that fans left their seats when it finished, wrongly assuming two games had been played in that amount of time and that it was a changeover.

Del Potro’s movement went from nimble to clunky after that. He had all but deflated.

“I was playing almost at my limit all the time, looking for winners with my forehands, backhands, and I couldn’t make them because Novak was there every time,” del Potro said.

On court, the match was defined by its many long rallies and impossibly powerful groundstrokes. Off court, it was a story of two comeback kids.

Del Potro was appearing in the second Grand Slam final of his career nine years after reaching his first. In the interim, he endured four wrist surgeries, including three on his left wrist, and contemplated quitting the sport altogether. He depended on his hometown friends, a group of whom have been in New York throughout the fortnight to lead cheers in Arthur Ashe Stadium, and worked his way back to the final at his favorite tournament.

Between the 2009 championship and Sunday, the Argentine competed in 22 Grand Slams, an Open era record for events between major finals.

While Djokovic laid on the ground in ecstasy Sunday, del Potro sat in his chair and cried.

“You can lose or win a trophy, but the love from the crowd, it’s could be even bigger than the tournament,” del Potro said. “That’s what I got from them. It will be in the heart for the rest of my life.”

At net after the match, Djokovic hugged his tearful friend. His injuries weren’t nearly as serious as del Potro’s, but his empathy and understanding of a hard journey was clear.

“I expected, to be honest, quite frank, after surgery that I’ll be back on a high level quite fast. But, you know, it took me actually three, four months really. In that process, I learned a lot about myself, learned to be patient, which was never really a stronger side of me,” Djokovic said.

“But at the same time, you know, life showed me that it takes time for good things. It takes time to really build them, for things to fall into place, so you can center yourself, balance yourself and thrive.”