AFTER six months out with injury and contemplating a clash with fifth seed Kei Nishikori, Roger Federer at first said he would be the underdog when they meet in the last 16 of the Australian Open today. And then he changed his mind.

There was a smile and then an attempted explanation but what came through above anything else is that the 17-time Grand Slam champion believes anything, even what would be a miraculous title win here, is possible.

It was during Federer’s straight-sets demolition of Tomas Berdych in the previous round that he really started to believe and when he plays Nishikori this morning, he will fancy his chances.

“Yeah, sure, he’s the favourite,” Federer said, before adding. “Maybe. I don’t know. It doesn’t matter. I still have to play Kei. Whether he’s the favourite, I’m the favourite, I don’t know. He’s definitely played better and more tennis in recent months. But then again, it’s a new season. We’ll see what happens.”

It might be five years since Federer won the last of his Grand Slams and this is his first official tournament since returning from six months out with a knee injury.

But the Swiss said he was looking forward to testing himself, mentally and physically against a man who reached the final of the US Open in 2014.

“I’m a big fan of his game,” Federer said. “He has one of the best backhands out there. I love how he can crush it down the line or cross-court. He has wonderful second-serve returns. He’s fast on his legs, strong in his mind. I know how tough he is as the match goes along. He finds his range and his rhythm, he’s tough to stop.

“We had a great match at the World Tour Finals a bit more than a year back. I’ve lost to him a couple of times as well. I’m aware of the big test for me. This one’s going to be completely different to Tomas. Not so much just serving, serving, serving, but there are going to be more rallies, even though the surface remains fast. I said it at the start of the week, it’s not easy to control the ball. When you serve well, it pays dividends.”

Having been a bit slow out of the blocks in his first two matches, Federer began brilliantly against Berdych and never let up, maintaining a high level throughout.

“It’s a big relief,” he said. “But like I said at the beginning of the tournament, any result was going to be a good result for me, just because I can test myself in a match situation against professional players. That’s what it’s about for me this week.

“I was ready for a battle, five hours, something big. It had it all written over it. I was able to come through it in 1 hour 20, 1 hour 30, however long the match was. It’s a great feeling. I’ve definitely had this feeling before, where you feel like you’re probably not going to lose this one if you keep being focused.

“I think the top guys have done a great job of always protecting the lead. I’ve done it [against Berdych], like I’ve had to do so many times in my career.

“What’s nice about this one is it was unexpected for me, unexpected for a lot of other people apparently as well, and it was against a fellow top player.

“I did get nervous at the end. I still believed there will be that hiccup, it has to happen. It didn’t happen and I’m here now and it’s good.”

Nishikori said he expects nothing less than a tough match.

“For sure it’s not going to be easy,” he said. “It’s always great to play Roger. It’s a big challenge for me.

“I’m just happy to play him because I think we needed him on the Tour. I’m happy to see him back to 100 per cent.”