After two stellar years, the world number one has had a much trickier time of it in 2013.
The season began well with a third straight Australian Open title and victory in Dubai, but since then he has won just one trophy, ending Rafael Nadal's long winning run in Monte Carlo.
Nadal took revenge in a titanic struggle of a French Open semi-final, denying Djokovic a chance to win the title he needs to complete his set of grand slams.
Four weeks later the world number one was beaten by Andy Murray in the Wimbledon final, and over the last two weeks he has lost close matches against Nadal and John Isner in Montreal and Cincinnati.
But the Serbian is energised by being back in New York, where he has made three straight finals, and thinks grand slam tennis will bring the best out of him again.
He said: "I thought I played quite decent in these two weeks. Both matches that I lost were 7-6 and 7-5 in the third set, and in important moments I wasn't finding that maybe extra strength to be calm and to play the right shots.
"That's what happens. You go through these periods. But my confidence is still there. This is a grand slam, so it is different from any other event. I love playing grand slams.
"I have a very good record at the US Open in the last five or six years, so I really look forward to it.
"I like the centre court, I like the atmosphere, I like the spirit of the court, it's suitable to my style of game, and the whole buzz that you feel around the US Open and around these courts.
"It's something that makes me very excited and motivated to play my best. I have been preparing very hard. I had these extra few days after I lost in the quarter-finals in Cincinnati to get ready and give my all during these few weeks."
Djokovic still has a healthy-looking lead in the rankings but Nadal had no points to defend until February and appears destined to overtake the Serbian sooner rather than later.
Hard courts have traditionally been the Spaniard's weakest surface but he is unbeaten on them this year, winning Masters titles in Indian Wells, Montreal and Cincinnati.
Nadal has won six clay-court titles as well and, with his knee problems seemingly behind him for now, he has found some of the best form of his career.
The same cannot be said for Roger Federer, who is seeded only seventh after his worst season for more than a decade.
Assessing his two rivals, Djokovic said: "Nadal is definitely back, and he's playing maybe the best tennis that he ever has played on hard courts.
"He hasn't lost a match. He won three Masters events. He won in great style. He was very aggressive, and he seems like he changed a little bit his game.
"He stepped in a little bit more. He knows that now he has to be a bit more aggressive than he usually is because of, I guess, his knees and because hard court is not clay. It's not his favorite surface, it's faster.
"I'm sure he worked on that, and you could see that all the work he put in is getting results. He's definitely so far the best player this year. There is no question about it. The results are showing everything.
"And Federer, on the other hand, is having results-wise probably the worst year he had in the last 10 years.
"I'm sure he knows what he's doing. He's probably focusing on the grand slams, and that's where he wants to perform his best.
"It is unusual to see that he's number seven in the world after being so dominant and so consistent every year in the last 10 years, always being one or two in the world.
"But there are so many young guys now coming up after the generation of Nadal, myself, Murray, (Juan Martin) Del Potro. Now you have (Grigor) Dimitrov, you have (Jerzy) Janowicz, (Milos) Raonic.
"So this is a new wave of players, and this is kind of a life cycle and the way it goes.You can't always expect somebody to be at the highest level."