Roger Federer disappointed with Australian Open showing after scrappy second-round victory

The former world No 1 beat Noah Rubin 7-5 6-3 7-6 (7/3)

Federer could face Murray in the quarter-finals (Getty)

Roger Federer admitted to feeling disappointed after scrapping his way to a 7-5 6-3 7-6 (7/3) victory over America's Noah Rubin and into the Australian Open third round.

A straight-sets win in just over two hours hardly sounds like cause for dejection but Federer's fitness and usual finesse both appeared lacking here, against an opponent ranked 200th in the world, playing only the fifth grand slam match of his life.

The 17-time grand slam champion will hope greater rhythm returns with more time spent on court given he now faces a far tougher challenge against world number 10 Tomas Berdych.

"I was just not doing what I was trying to do. I was hoping to play better at times," Federer said.

"I think you can always do better. It's one of those sports like golf, you can always leave frustrated. Like tennis, you can feel: 'I could have always played a little bit better'.

"At the end of the day you have to be happy with what you did, as well. I have to be happy with the little things.

"Sometimes it's not going to be pretty. Sometimes it's just going to be a fight. Today that's what I thought it was for me.

"I guess I was hoping to play better offensive tennis and I struggled with that a little bit at times."

All of which will be music to the ears of Berdych, who has lost his last five meetings with the Swiss but showed impressive efficiency in dispatching American Ryan Harrison earlier on Wednesday.

"I know I've got to lift my game a little bit," Federer said.

Federer admitted he was left frustrated with his performance (Getty)

"I thought he was going to have a tougher time against Ryan, to be honest, because Ryan has been playing well recently again.

"The court here plays fast and he's caused difficulties for me in the past on faster courts - Cincinnati, New York, Wimbledon, the Olympics in Athens - I know what he's got. I don't need to tell you where he's beaten me."

It certainly was not all doom and gloom for Federer who, after skipping the second half of 2016 to recover from injury, was playing only his second competitive match since Wimbledon.

"If I could have signed this to be in the third round, feeling this way, weeks or days or a month ago, I would have taken it," Federer said.

Wawrinka could face Britain's Dan Evans in his quarter-final draw (Getty)

"I'm still hoping to feel better and better and better as we go along."

Federer's compatriot Stan Wawrinka rebounded from his opening five-set marathon against Martin Klizan to ease past American Steve Johnson 6-3 6-4 6-4, while fifth seed Kei Nishikori also cruised through, beating Frenchman Jeremy Chardy 6-3 6-4 6-3.

There was nothing straightforward, however, about the passage of Germany's Mischa Zverev, who beat another American John Isner 6-7 (4/7) 6-7 (4/7) 6-4 7-6 (9/7) 9-7 after four hours and 10 minutes.