Former tennis player Greg Rusedski believes although the Big Three are the players to beat at the US Open, Roger Federer's confidence is affected a bit by his Wimbledon quarterfinal loss last month.

Federer looked on course to win his 21st Grand Slam at Wimbledon but would surrender a two-set lead as well as match point to lose to eventual finalist Kevin Anderson in what was one of the shocks of the year.

In the buildup to the US Open, the Swiss legend would just take part in the Cincinnati Masters but would lose to Novak Djokovic in two sets in the final.

Djokovic's wins at Wimbledon and Cincinnati, meanwhile, have made him the favorite at Flushing Meadows, and Rusedski agrees, even stating he could be back in the conversation for the GOAT accolade, particularly after a forgettable 2017.

"At this rate, Djokovic is on track to put himself back in the conversation for the Greatest of All Time – or GOAT, as the shorthand goes," he wrote in his Telegraph column. "Yes, he is still seven slams behind Federer, in first place. But remember what he can do when he is on his game."

"In 2011-12, he won three majors in a row. In 2015-16, he extended that to a scarcely believable four in a row – an achievement that has yet to receive the acclaim it deserves."

Defending US Open champion Rafael Nadal is the second favorite for Rusedski and Federer is just behind the duo, but it's not just because of his defeat to Anderson but his hard-court preparation as well.

"I would put Rafael Nadal as the next-most-likely winner, and Federer in third place, because I feel that Roger’s confidence has been rocked a little by his loss to Anderson at Wimbledon," Rusedski added. "Federer restricted his hard-court preparations for the US Open to just a single tournament, the Cincinnati Masters."

"This reduced schedule is probably the right thing for his body, but it restricts his ability to build momentum and match toughness."

Federer would go on to win his opening round game against Japan's Yoshihito Nishioka on Tuesday quite comfortably since Rusedski's column; however, the real gauge of his confidence will come when he faces a top 20 opponent.

The 37-year-old though, admitted he was happy not to be nervous in his win over Nishioka and Rusedski believes the performance was a good sign.

"I thought he flowed incredibly well for two and a half sets," Rusedski said. "A little bit of hiccup, but I think he will be very pleased with his start at these Championships. All those Federer fans who were worried after Cincinnati, it looks like his mojo is coming back nicely!"

Federer faces France's Benoit Paire next in the second round.

There were no upsets elsewhere either as Djokovic and Nadal all came through their first round ties. The US Open will take place until Sept. 9 when the men's singles final will be contested.