Djokovic clinched his third US Open title on Sunday with a 6-3, 7-6 (7/4), 6-3 triumph over del Potro, taking him level with Pete Sampras's mark of 14 Grand Slams.
Djokovic said he believes del Potro will win another major title.
This was Djokovic's third championship in NY, along with those in 2011 and 2015.
After seizing an early break in the second set, Djokovic suddenly found himself on the run, dropping three straight games before he dug in to salvage a service hold in a 20-minute marathon game that went to deuce eight times.
Djokovic, the No. 6 seed, missed this tournament previous year as he struggled with an elbow injury that ultimately required surgery.
For Del Potro, it was a heartbreaking experience coming in just his second Slam final, nine years after he was crowned US Open champion.
Something in the Alpine air clearly agreed with him, though, and he went on to triumph at Wimbledon, the US Open tune-up in Cincinnati, and then in NY to grab his 14th career Grand Slam title, putting him third on the all-time list.
Juan Martín del Potro brought his own cheering section to the US Open, but in truth, the "gentle giant" from Argentina has the backing of the entire tennis world.
But instead of that victory proving a launchpad for a sustained challenge at the Grand Slams, Del Potro battled wrist injuries which required four surgeries.
After an overhead smash on match point, Djokovic dropped to his back in elation before embracing del Potro at midcourt. "I'm glad that Novak is the champion".
This year, del Potro won his maiden ATP Masters 1000 title in Indian Wells - beating Federer again - made his second Roland Garros semifinal and posted his best Wimbledon result (quarterfinal) since 2013.
Del Potro's sole Grand Slam title came at the U.S. Open in 2009 and he said it had been an emotional journey back to the Flushing Meadows final.
"Difficult times but you learn from adversity. when you have doubtful moments when things are not working out as you want (them) to and I try to take the best out of myself in those moments and thrive on the love and support I receive from my closed ones and get myself in this position", Djokovic expressed.
"There is a lot of significance of me being now shoulder to shoulder in terms of Grand Slam wins with him".
"When I had the surgery of my elbow earlier this year, I could truly understand what Juan Martin was going through with his surgeries for 2-3 years that kept him away from tour".
Osaka has never been to Nemuro, but she is said to have expressed a desire to visit the place where her mother was born, although her grandfather commented, "She'll be busy and I guess it will be hard for her (to come soon)".
With the Arthur Ashe Stadium roof closed as heavy rain swept NY, conditions were slow and sluggish.