It seems laughable now that in the days leading up to the US Open there were plenty of people willing to write off Novak Djokovic's chances of winning the title.

As New York prepares for the semi-finals here today, those people are probably busy hiding their faces.

The effort and performance of Roger Federer in recovering from two sets down and later two match points down against Gael Monfils may have increased talk of a possible record 18th grand slam title for the 33-year-old Swiss.

But such talk should surely be shrouded in the reality that world No.1 Djokovic, having disposed of Andy Murray in an outstanding quarter-final, is the overwhelming favourite to add this year's US Open title to his Wimbledon crown.

Watching him soak up everything Murray could throw at him was a masterclass in movement and the ability to turn a losing position in a rally into a winning one.

Australian Darren Cahill, the part-time coach and now a pundit for ESPN television, said Djokovic's movement is unparalleled.

"He's a joke, the way he can cover the court," Cahill said. "There were a number of times there where he turned defence into offence with one single shot out of nowhere.

"Andy played seven or eight great shots that would have won points against just about anybody else and then with one ball loses the point.

"That's heart-breaking when you're playing against a guy who can do that, because then you have to make adjustments. You feel like: 'OK, I'm going to put all this work into a point just to lose it? If I'm going to lose the point I'd better lose it with the third shot rather than 12th shot.' That's the psychological barrier you have to get through when you play a guy like Novak.

"I picked him to win it and I am sticking with him."

It was a couple of early defeats in Toronto and Cincinnati that caused people to doubt Djokovic's title chances, even though he had won Wimbledon just a month beforehand. Having got married just after Wimbledon and with the impending birth of his first child, Djokovic could be forgiven if he had taken his eye off the ball.

But the idea was always to get himself ready, physically and mentally, for the final grand slam event of the year and he appears to have done that perfectly.

"I was aiming to play my best tennis in the US Open and I believed that was going to happen.

"I'm really glad that I'm in another semi-final here, after a tough draw, with some tough players.

"Of course as the tournament progresses I'm trying to gather together as much confidence as I can. Winning against Andy in a grand slam is definitely a confidence boost, and hopefully I can use it for the next match."

That next match is against Nishikori, who is into his first grand slam semi-final and finally fulfilling the potential he has shown over the past few years. The first Japanese man to reach a slam semi-final since 1933, Nishikori faces a tough task to recover from back-to-back four-set, four-hour matches.

Logic says Djokovic will run him ragged but the Serb said he would be wary of taking anything for granted against an opponent he says is playing "the best tennis of his life in the past 12 months".

"He started working with Michael Chang and he changed a few things in his game," Djokovic said.

"He serves very efficiently. Obviously he's very, very fast, maybe one of the fastest on the Tour. Great backhand, great forehand, all-around player.

"I give him credit for that. We both had some long matches in quarters. The better [player] will win."

Federer should be buoyed by his great escape against Monfils but will also need to bounce back from a five-setter and have enough energy to face a rejuvenated Marin Cilic, the Croatian who is in his second grand slam semi-final, four years after his first. "I must say he's really cleaned up his game," Federer said of Cilic, who has added power to his serve under the guidance of former Wimbledon champion Goran Ivanisevic. "He's done well in the past, it's not like he's come from a top-50 player to all of a sudden knocking on the top-10 door."

"I played him in Toronto [last month]. Funny match, I didn't play great in the first set but somehow got it done, and then I think I wasted like eight match points in the second set; had to go three. It was late at night, 12:30 and [you think], do I really have to do this? But that's exactly what got me through in Toronto to win Cincinnati and be in the situation today and facing Marin. So it was good to beat him. It's going to be a tough match."