AP Photo Rafael Nadal reacts after defeating Daniil Medvedev to win the men’s singles final of the U.S. Open tennis championships Sunday.

NEW YORK (AP) — Rafael Nadal’s 19th Grand Slam trophy went from inevitable to suddenly in doubt in a thrill-a-minute U.S. Open final.

What had all the makings of a casual crowning morphed into a grueling contest thanks to Nadal’s opponent, Daniil Medvedev, a man a decade younger and appearing in his first major title match. Down by two sets and a break, Medvedev shifted styles, upped his level against a rattled Nadal — and even received an unexpected boost from the Arthur Ashe Stadium spectators.

Truly tested for the only time in the tournament, the No. 2-seeded Nadal managed to stop Medvedev’s surge Sunday and hold off his historic comeback bid, pulling out a 7-5, 6-3, 5-7, 4-6, 6-4 victory in 4 hours, 50 minutes of highlight-worthy action and Broadway-worthy drama to collect his fourth championship at Flushing Meadows.

“One of the most emotional nights of my tennis career,” said Nadal, who covered his face with his hands while crying when arena video boards showed clips from each of his Slam triumphs.

“The last three hours of the match have been very, very intense, no?” Nadal said. “Very tough mentally and physically, too.”

Now at 19 majors — a total Medvedev called “outrageous” — Nadal is merely one away from rival Roger Federer’s record for men.

But this one did not come easily. Not at all.

Sure seemed it might, with Nadal ahead by two sets and a break in the third at 3-2, playing like “a beast out there,” as the No. 5-seeded Medvedev put it.

At that moment, Medvedev would joke afterward, this is where his thoughts were: “OK, in 20 minutes I have to give a speech. What do I say?”

But the 23-year-old from Russia did not go gently into the night. He broke right back to 3-all, then again to claim that set and yet again to end the fourth.

“The nerves were so high,” Nadal said. “A crazy match.”

Not since 1949 has anyone won a U.S. Open final after trailing by two sets to none. Never before had Medvedev won a five-set match. Only once before had Nadal lost a Grand Slam match after taking the opening two sets.

And yet the tension was real.

At the very end — or what appeared to be the very end — Nadal couldn’t close it out. After breaking to lead 3-2 in the fifth, in a game Medvedev led 40-love before flubbing an easy forehand, Nadal broke again and served for the championship at 5-2.

The way this back-and-forth tale was spun, though, it probably was inevitable that Medvedev would break there. And so he did, because Nadal double-faulted on break point after he was docked a serve for his third time violation of the evening, which elicited loud boos from folks in the stands.

In the next game, Nadal held a pair of match points, but Medvedev, of course, avoided defeat yet another time, erasing one of those with a backhand winner, the other with a service winner, earning a standing ovation.

With Nadal’s backers screaming, “Close it out!” at the ensuing changeover, he once more stepped to the baseline to try to serve it out, this time at 5-4. Naturally, he was forced to deal with another heart-in-throat break point, but came up with a stinging forehand that drew a long forehand from Medvedev.

Two points later, it was over, and the indefatigable Nadal was splayed on his back on the court, as he’s been so often at the conclusion of energy-sapping, will-challenging, high-stakes matches.

“What he went through during the match and still being able to survive and finish the match that way, it’s out of this world,” said one of Nadal’s coaches, Carlos Moya. “You have to be, mentally, a genius. He’s still there, still fighting and turning things around when things look really bad. He was able to do that today.”