He almost quit tennis in 2015, after four wrist surgeries that wouldn't let him regain the form that carried him past Roger Federer to win the 2009 U.S. Open.
Djokovic equalled Pete Sampras's tally of 14 major titles when he overcame Juan Martin del Potro in three closely fought sets - 6-3, 7-6, 6-3.
That pressure told in game eight, leaving Djokovic needing just a regulation hold to claim a superbly crafted third US Open title.
Millman's upset win against Roger Federer, regarded by many as the best player of all time, in the fourth round of a grand slam was a career highlight for the proud Queenslander. The only two players with more Grand Slam titles than him are Rafael Nadal (17) and Roger Federer (20).
Even Del Potro suggested that Djokovic could one day surpass Federer, who is six years older than 31-year-old Djokovic.
Juan Martin del Potro was gracious in defeat and said Djokovic can end his career as the most successful Grand Slam title victor, surpassing Roger Federer's current mark of 20. He was soon 3-1 up in the second set before Potro carved out his first break point of the match to level at 3-3.
In all, the second set was a lengthy 95-minutes before ending for Djokovic in the tiebreaker, and saw both players leave the court for a change of clothes at its conclusion. After the third round, he did not lose a single set as he was able to outlast a fan favorite in Del Potro.
He added: "I would like to congratulate Juan Martin".
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She said: "For me, Novak, the only difference is sometimes mentally he checks out".
It was only the second set dropped by the Argentine at the tournament.
It is the third U.S. Open title of Djokovic's career, and his 14th overall Grand Slam win.
The second set tie-break proved to be the turning point as the Serbian took it and from that point on, his victory on Arthur Ashe Stadium looked inevitable. Eventually, he seized that game - and del Potro's best chance to make a match of it. I had my opportunities during the second and third set but I was playing nearly at the limit all the time ... and I couldn't make it because Novak was there every time.
'I don't know the answer.
This time past year Djokovic was injured and uncertain about his future direction. "She gave me some experience to play the final, because she played in the Australian Open final". That put the 29-year-old Argentine back in a Grand Slam final for the first time since his breakthrough nine years ago, a comeback for a guy who had four wrist operations in the interim.
Last year is the only time in the last eight years he failed to pick-up at least one major trophy in a season.
Djokovic continued a remarkable summer after missing the end of last season with a right elbow injury.