After Del Potro made it past an injured Rafael Nadal, who retired when trailing by two sets, Djokovic looked superb as he romped past Kei Nishikori to reach his eighth final at Flushing Meadows.

High on confidence after his Wimbledon triumph in July, the Serbian will undoubtedly start as the favourite against Del Potro on Monday (AEST).

Yet the in-form Djokovic, who has a 2-5 record from his previous finals in New York, expects a stern test from the 2009 champion, who has also looked in tremendous form over the past fortnight.

"I personally like him very much, not just as a player but as a person," Djokovic said of Del Potro. "He's a dear friend, someone that I respect a lot.

"We all felt for his struggles with injuries that kept him away from the tour for two, three years. But he was always a top-five player in the eyes, I think, of everyone. We all knew that he had a capacity and a quality to get to the point where he is at the moment. It was just a matter of time.

"I saw before the match against Nadal that he's the player that had the most wins against world number ones [without ever topping the rankings himself]. That shows the quality that he has, especially in the big matches. He's a big-match player. He's a grand slam winner. He's playing the tennis of his life."

Discussing Del Potro's obvious strengths, Djokovic added: "He always possessed that big forehand, [and a] big serve. His game kind of revolves around that.

"He has alternated his backhand over the years because of the left wrist injury. But I think now he's more comfortable with it. When he was coming back from surgery, he struggled a lot with the high balls or low balls, trying to kind of play very flat. Now it seems like he's found the range.

"One of the keys of the match will be [my] return, how well I can return, how many returns I can get back in play, but also try to have some depth in that return, and how accurately I can serve myself.

"I think that's very important. When you play a big server like Del Potro, you feel pressure also on your service games."