Novak Djokovic has erased any doubts over his form with his opening-round strolls at the US Open, Greg Rusedski told Sky Sports.
World No 1 Djokovic was dumped out at the last-16 stage of the hard-court events in Toronto and Cincinnati following his Wimbledon triumph over Roger Federer in July.
But the Serb has breezed into round three at Flushing Meadows with comprehensive wins over Diego Schwartzman and Paul Henri-Mathieu and smashed 13 aces in his victory over the latter on Thursday night.
“He was very impressive – and the questions marks have been answered,” Rusedski said of Djokovic, who is targeting a second US Open crown having won the title in 2011.
“He has been very ruthless and very efficient, not dropping a set so far, hitting lots of aces and moving very well on the court.
“He seems very relaxed, which is always a good sign, and he is back in the form he was in when he won Wimbledon.
“It is going to get tougher from here on in because he faces the big-serving Sam Querrey next and then most likely John Isner and Andy Murray, but he is looking very good.
“He is the best returner of serve in the world by far and his backhand is sensational, but when the forehand is functioning, too, it becomes a key element.
“It is certainly functioning at the moment and his serve has become real weapon as well.”
Murray, meanwhile, remains on course for a last-eight showdown with Djokovic after seeing off German qualifier Matthias Bachinger in straight sets in round two.
The 2012 US Open champion, who battled cramp en route to defeating Robin Haase on Monday, won 6-3 6-3 6-4 at Arthur Ashe Stadium to secure a last-32 clash with Andrey Kuznetsov.
And the Scot, who may have to conquer Jo-Wilfried Tsonga, Djokovic, Stan Wawrinka and Roger Federer to land a third Grand Slam title, earned praise from Boris Becker for the way he dispatched the dogged Bachinger.
“I am going to give Andy 9.5 out of 10 because it was a very solid performance,” said Becker, Dkokovic’s coach and the 1989 US Open champion.
“He was challenged in the third set a little bit – he was down break points at 2-2 and had a long game at 3-3 – but he kept raising his level.
“He felt comfortable on the court, and will be happy the match lasted less than two hours.”
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