The 31-year-old beat Argentinian world number three Del Potro with a 6-3, 7-6 (7/4), 6-3 taking him level with Pete Sampras´s mark of 14 Grand Slams.
The disappointment on Sunday belonged to a teary Del Potro who was back in a Grand Slam final for the first time since the big Argentine won his one and only title at Flushing Meadows in 2009.
A focused Djokovic continued to apply pressure in the third set until Del Potro finally cracked on serve to fall behind 5-3, with the Serb closing out the match with a ferocious overhead victor.
This time Djokovic is No.3 behind Nadal and Federer, but the stunning three-year first will have tennis fans asking if it really is 2018.
He missed last year´s tournament with an elbow injury which sent his career into a mini-crisis. When they shout "Ole, ole, ole, ole", that's what I hear.
Even his rival for the US Open title, 13-time Grand Slam champion Novak Djokovic, has a hard time rooting against del Potro, the 2009 US Open victor who has painstakingly rebuilt his career after years of wrist injuries threatened to derail it.
Del Potro spoke this week about the low point, in 2015, when he considered quitting the sport. Since the start of Wimbledon, Djokovic has only lost a match and has won two Grand Slam title and the Serb thanked his support system for it.
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Even the International Tennis Federation (ITF ), which stood by the judges, waited 48 hours before announcing a position. Naomi Osaka dropped by " The Ellen DeGeneres Show " on Wednesday, opening up about everything from her historic U.S.
If Del Potro relies heavily on power, Djokovic, fresh from winning the Wimbledon title two months ago, is a master tactician who never gives up on a point.
A costly double-fault from Del Potro - his first of the match - and a series of errors saw Djokovic move one game away from victory and after three hours and 16 minutes he completed the job with an unstoppable overhead smash and then lying flat on his back on the court in celebration.
Del Potro, 29, won the only Grand Slam title of his career by upsetting Federer in NY in 2009, but couldn't swing the upset Sunday. "Today I really am".
Nadal stayed at No. 1 despite retiring from his semifinal last week, and Federer remained No. 2 after a fourth-round loss in NY.
Novak Djokovic says he thinks the chair umpire interfered too much in Serena Williams' match but stopped short of saying men and women are treated differently.
"He is more hard to move, skidding and changing direction because of the height, so I tried to get rid of him as much as possible". "I believe he'll be here again with the champion's trophy".
With his third championship at Flushing Meadows, Djokovic matched Pete Sampras for third on the career list for Grand Slam titles. He depended on his hometown friends, a group of whom have been in NY throughout the fortnight to lead cheers in Arthur Ashe Stadium, and worked his way back to the final at his favorite ATP Tour event.