The US Open final appeared to be slipping away from Novak Djokovic when he dropped three consecutive games.

He was angered by a crowd roaring for his popular opponent, Juan Martin del Potro. He was, in short, out of sorts.

And then came Sunday’s pivotal game, a 20-minute, 22-point epic.

Three times, del Potro was a point from breaking and earning the right to serve to make it a set apiece.

Three times, Djokovic steeled himself. Eventually, he seized that game and del Potro’s best chance to make a match of it.

A year after missing the tournament because of an injured right elbow that would require surgery, Djokovic showed that he is unquestionably back at his best and back at the top of tennis.

The Serb collected his 14th grand slam title and second in a row by getting through every crucial moment for a 6-3 7-6 (7-4) 6-3 victory over del Potro.

This was Djokovic’s third championship in New York, along with those in 2011 and 2015, as he drew even with Pete Sampras on 14 major to be third all time – trailing only Roger Federer (20) and Rafael Nadal (17).

“I was hoping he was going to be here, but he’s not,” Djokovic said about Sampras. “He’s my idol. Pete, I love you.”

Del Potro was in his first slam final since his 2009 success at Flushing Meadows, after four wrist operations in the interim.

“I believe he’ll be here again with the champion’s trophy. I really do,” Djokovic said.

Djokovic was better than del Potro on their many lengthy exchanges, with the roof closed on Arthur Ashe Stadium because of rain.

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

When it ended, thanks to a three-game closing run by Djokovic, he flung his racquet away and landed on his back, arms and legs spread wide.

“When I had the surgery in my elbow earlier this year, I could truly understand what Juan Martin was going through,” Djokovic said.

“Difficult times, but you learn through adversity.

“I try to take the best out of myself in those moments.”

A gloomy season that started with elbow surgery after the Australian Open is turning into a brilliant finish for the 31-year-old Serb, who has now won three of his past four events including back-to-back slams at Wimbledon and Flushing Meadows.

Over the past eight weeks Djokovic has resembled the player that held all four major titles at the same time in 2016 and the $3.8 million ($A5.3 million) winner’s cheque lifted him above Federer as the leader in career prize money.