Serbian Djokovic, the defending champion, outlasted Frenchman Gael Monfils 6-3, 6-2, 3-6, 6-2 as his opponent resorted to unusual tactics to try and unsettle the world number one.

In extreme heat, Monfils attempted to slow play down with light shots and a lack of movement after losing the first five games of the match, leading to criticism from the likes of American legend John McEnroe.

Djokovic was briefly affected but in the end was too strong.

The 12-time Grand Slam champion has benefited at this year's tournament from three retirements and will presumably be fresher than normal for Sunday's (September 11) final.

"Well, it was a strange match, as it always is, I guess, when you play Gael, who is very unpredictable player," said Djokovic.

"I was completely caught off guard when he just stood there and chipped the ball back and didn't do much."

Monfils defended this tactic, saying: "I'm just embracing the fact the guy is too good for me, and I try to switch strategy.

"Is not academic, but I try to win.

"I think I'm gutsy to try that, you know, against the number one of the world."

Two-time winner Djokovic has moved into his seventh US Open final and will be looking to win three of the four Grand Slams inside a calendar year for the second season in a row.

Swiss player Wawrinka booked his spot against him by beating Japan's Kei Nishikori 4-6, 7-5, 6-4, 6-2.

The former French and Australian Open champion will be looking to add a third major title to his CV.

"Kei is a tough player and he played well from the beginning," said Wawrinka, the number three seed.

"I had to wait and fight and make him a bit uncomfortable and he started to get tired.

"That is when I put my game to be aggressive. 

"To be in the final is crazy."

The women's final between Czech player Karolina Pliskova and German Angelique Kerber will take place tomorrow.