Father-to-be Novak Djokovic admits tennis no longer comes first, but the world No.1 is still strutting around New York feeling very much like the US Open favourite he is.

With Rafael Nadal unable to defend his crown and Djokovic struggling to shake his post-Wimbledon and wedding hangover, the resurgent Roger Federer is many people’s pick for title No.6 at Flushing Meadows.

Third-round defeats in Toronto and Cincinnati, where Federer reigned supreme, have cast doubts about Djokovic’s physical and mental state of mind heading into the season’s final major.

But while the Serb concedes to have been “emotionally a bit flat” following his marriage to long-time girlfriend Jelena Ristic after conquering Federer in their classic five-set Wimbledon decider, Djokovic insists the honeymoon’s now over.

A five-time Open finalist and champion in 2011, Djokovic is top seed this year and, despite the recent on-court setbacks and off-court commitments, is planning another successful campaign.

“I have high expectations for myself,” Djokovic said before facing Argentine Diego Schwartzman in the first round on Monday.

“I always have, especially at this stage of my career where I feel like now is the time that I’m at my peak physical strength.

“I want to use this time of my career as much as I can to win as many matches as possible.

“This is the last grand slam of the year, and this is where you want to play your best.”

Djokovic, though, hasn’t won many matches lately and concedes the last two months have been a “very emotional period”.

The 27-year-old also knows life is about to change forever with the birth of the newly-weds’ first child, due in October.

“I’m going to enjoy it and try to take as much energy as I can, positive energy to (try and) kind of transfer that to the tennis court,” he said.

“But, without a doubt, life changes. Priorities change. My priorities, you know, my family, my wife, my future kid – tennis is not definitely not No.1 anymore.”

With four children – and two sets of twins no less – Federer knows better than any player on tour how to juggle parenting with the demands of professional sport.

But tennis’s big daddy isn’t about to offer his great rival any fatherly advice, other than good luck with that.

“I wish him well,” the second seed said ahead of his first-round clash with Australian Marinko Matosevic on Tuesday.

“It’s normal, I think, when you’re entering the whole family thing that many people you talk to, all you talk about is babies and how to prepare for it mentally.

“It’s a very exciting time and, with the wedding and everything, I’m sure he’s going through a great spell at the moment with winning Wimbledon on top of it.

“So things are great for him, but I think he’s got to figure it out himself really.”

That said, Djokovic has been one of the few to figure out Federer’s majestic game this year.

The Swiss is back to full confidence, free of the doubts and injury that led to his leanest season in more than a decade last year.

After winning only 45 matches in all of 2013, Federer boasts a tour-best 49 already in 2014 and, at 33, fancies his chances of becoming the oldest man’s grand slam champion in more than 40 years.

“Last year I was trying to convince myself I did have an opportunity,” he said.

“This year I played a lot of good matches … everything seems so simple.

“It’s nice feeling that way. I really feel like I can play a great tournament.”