It might not have been a five-set grand slam classic, but the thrill-a-second match lived up to expectations as a fitting bookend to a rainy championship.
"It really sounds unreal. It's an incredible, incredible feeling," said Djokovic, who beat Nadal in a final for the sixth time this season. "I've had an amazing year and it keeps going."
In a rematch of last year's championship match, which Nadal won in four sets, Djokovic rallied from 0-2 deficits in the first two sets and fought back after dropping a third-set tiebreaker to win 6-2, 6-4, 6-7 (3-7), 6-1.
Djokovic became the sixth man in the open era to win three grand slam titles in the same season, running his overall record in 2011 to 64-2, including 10 tournament victories.
"This guy's doing unbelievable things," said Nadal, who looked overmatched in the final set even after Djokovic needed medical attention several times for a back injury.
The 24-year-old Serbian also beat Nadal, 25, in this year's Wimbledon final, snatching Nadal's No. 1 ranking in the process. He claimed his second Australian Open win earlier this year and now boasts four grand slam titles.
On Monday, he climbed out of early holes by consistently breaking Nadal's serve, including an almost 20-minute game in the second set that featured eight deuces.
When the match ended after 4 hours and 10 minutes, with Djokovic hitting one last forehand winner to finish it, Nadal was left wondering how much more he could have given.
"These kind of matches are very difficult," he said. "It brings your body to the limit."
The No. 2 seed, Nadal remained on 10 career grand slam titles and 46 singles victories. The Spaniard became the seventh man to complete the career Grand Slam when he defeated Djokovic last year in Flushing Meadows.
But Djokovic has been a different player this season, almost unbeatable during certain stretches. Indeed, the only grand slam he didn't win was the French Open, which Nadal captured.
"I won a lot (against him) in the past," Nadal said Monday, "and the only thing I can do is try my best every day to keep improving."
It was the fourth straight year the U.S. Open ended on a Monday because of rain. Djokovic received a $1.8 million first-place check for his 28th singles title, while Nadal earned $900,000 as the runner up.
Djokovic improved to 13-16 lifetime against Nadal, and 2-5 in grand slam matches, but needed early rallies in the first two sets Monday to take control.
Hours in, Djokovic served for the match at 6-5 in the third set, but played from behind the entire game, eventually hitting a forehand wide on the final point.
Nadal jumped out to a 2-0 lead in the tiebreaker on errant shots by Djokovic, then built a 5-1 lead by shuffling into the middle of the court for a forehand winner. Djokovic clawed within 5-3 on a service winner and a strong backhand that Nadal returned into the net.
But Nadal followed with a backhand winner on a point Djokovic seemingly gifted the Spaniard by not hitting into the open ad side, and Djokovic hit a forehand into the net to lose the set.
Afterward, Djokovic lay flat on his stomach next to the court as an event trainer tended to his back. Djokovic also needed time after taking a 1-0 lead in the fourth set.
Djokovic won the fifth break point in the next game, firing a deep forehand winner to the ad side, and then served for a 3-0 lead. The match reached the four-hour mark as Nadal served to get within 3-1.
It was the last game he won.
Up 4-1, Djokovic broke Nadal in four points to serve for the match. He took a 30-0 lead in the last game with a couple of strong forehands, then later hit a backhand winner for 40-30.
Djokovic collapsed on his back after winning the last point with a smashing forehand winner.
"It was obvious that he was physically fitter than me on the court today. I knew that," Djokovic said. "I had to go for my shots, and I did."
Earlier, after falling down 2-0, Djokovic rallied to win six games in a row in the first set while breaking Nadal's serve three straight times. Nadal broke Djokovic early in the second set, just as he had done in the first, to take another 2-0 lead.
The marathon third game featured eight deuces and some of the most breathless points in the match -- almost none better than the last. During it, Djokovic hit a virtuoso defensive lob that drove Nadal back to the baseline and turned momentum in his favor.
Nadal eventually hit an overhead into the net, and Djokovic held serve to tie the set at 2-2. He earned another break to make it 3-2 when Nadal double- faulted on game point, and then served for a 4-2 lead. The seventh game featured four deuces before Nadal finally closed it out.
Following a pattern, the next game went to deuce before Nadal broke Djokovic with a blistering backhand down the line to tie the set at 4-4, pumping his fists out in front of him when the point was over.
But Djokovic broke Nadal right back, serving to win the second set 6-4, then broke Nadal to take a 2-1 lead in the third set.
Later, Nadal broke Djokovic in four points to tie the third set 3-3, clinching the game with a smashing forehand winner. Nadal lost just one point on his next serve -- Djokovic's impossibly angled backhand return on the ad side -- while taking a 4-3 lead.
Bouncing back, Djokovic aced Nadal at 40-30 to even the set at 5-5 and then broke him to go ahead 6-5, winning a long point at the net before closing out the game with a deep backhand to the deuce side of the court.
Monday marked only the 11th time in the open era, and first since 1996, that the top two seeds played in the U.S. Open final.
Djokovic, who was the 2007 runner-up to Roger Federer, also beat Nadal in lucrative finals at Indian Wells, Miami, Madrid and Rome this season. He saved two match points against Federer in the semifinals on Saturday.
Djokovic wore a navy blue FDNY hat before and after Monday's match, taking time afterward to mention Sunday's 10th anniversary of the September 11 attacks. He said how lucky they were to be playing tennis for a living and how other things mattered more.