WE don't know how he did it, but he did.

At 35-years-old and having only just returned from a six-month injury lay-off, Roger Federer is a grand slam champion once more.

The Swiss maestro picked up major title number 18 after an epic win over Rafael Nadal in Sunday night's Australian Open final. He needed five sets, three hours and 37 minutes and a whole bag of tricks to get there, but once again he showed why he has every right to be classified tennis's greatest of all time (GOAT).

In a match that had more momentum shifts than John McEnroe blow-ups, the thriller was the perfect manifestation of the Federer-Nadal rivalry that has gripped the tennis world for more than a decade.

Neither Federer nor Nadal were supposed to be on court on January 29.

Their ageing bodies should have let them down. The fact they'd hardly been able to play in 2016 should have meant they were rusty and unable to keep up with younger, more battle-hardened opponents.

Federer admitted as much in the post-match presentation.

"I'm out of words ... I'd like to thank Rafa on an amazing comeback,” Federer said. "I don't think either one of us thought we were going to be in the finals in Australia when we saw each other at his academy five months ago.

"I would have been happy to lose to be honest, the comeback was perfect as it was. There are no draws in tennis but if there was I would have been happy to draw and share it with Rafa, really.”

Yes, the comeback was perfect. Not just in terms of the end result, but because that result came against the Swiss' greatest rival.

The world No. 17 was aiming low before the start of the year's first grand slam, but as he progressed - winning three five-setters in a major for the first time in his career (including earlier wins over Kei Nishikori and Stan Wawrinka) - the motivation to achieve something he will never forget drove him forward.

In a career full of highlights, a "milestone” is how the fan favourite described this particular triumph.

"I would have said a great event would be quarters, you know. I said fourth round would be nice, quarters, great,” Federer said. "I went so much further than I thought I would. Today I just drove myself forward.

"It is all worth it. You don't know if they ever come back, these moments. That is what you work hard for. You work for the stress and you work for it to go away and you work for it for maybe a country, for Switzerland, maybe for your team, for your family, for whatever it is.

"It's a milestone in my career. This one means a lot to me because he (Nadal) has caused me the most problems over the years. So to get one over him in the fifth set is incredible, absolutely and feels super special.

"Of course there's stress that goes away and it is just emptiness and this beautiful moment. I couldn't be happier right now.

"I can't believe I'm sitting here and doing all this. It's incredible, it really is.”