R Fed is not here to put boots on caterpillars and tucks away a love hold to get back to the task of trying to win a break back.

Ten minutes ago Nishikori was on the cusp of going a break down and probably waving goodbye to the Aussie Open.

Now he's break up and coasting through his service game 40-15.

Sliding doors and all that...

Blimey guvna, where'd this come from?

Nishikori picks out a kick-up serve with microscopic vision and pummels the winner.

A couple of challenges draw the crowd into the action - not that this match needed it - and Kei lands a passing forehand down the line for a break out of nowhere.

Nathan: I can't believe what I'm seeing. Federer knows he's 35 right?  

Sandra: Come on Roger - you can do it  

Like Wile E Coyote on the edge of a cliff, Nishikori's fingernails are scraping off the precipice one by one in this match.

Federer is on the Nishikori second serve like Father Christmas on a mince pie and keeps slapping it back with interest.

The Swiss scores one backhand winner from almost in the front row of the Rod Laver Arena.

We go to deuce umpteen times - with Nishikori surviving a raft of break points - and there's a gritty, gutsy hold.

June: Wouldn't it be fantastic if Roger won this?  

You can say that, June. I, on other hand, cannot.

Federer unleashes Go-Go Gadget Arms at the net to dab back some unlikely volleys - but Nishikori finally finds the pass. It's a rare high for Kei though.

It sums up the movement of the 17-time Grand Slam champ though, as the Japanese is made to work so hard just to stay in points.

Image source, Reuters

The umpire is on the blower - possibly calling in the trainer for Nishikori.

The Japanese double faults for 0-30 and bounces his racquet off the floor in anger - it boings back into his hands so he does it again for good measure.

Has he released some venom? This is a ridiculous crosscourt winner from the fifth seed to get back to 30-30.

And Federer finds the net twice for a huge hold from Kei.

Image source, Reuters

A big old Federer ace to get us going in the fourth.

But here's a chocolate-smothered back hand down the line from Nishikori to show he means business.

But three more aces - 16 in the match now - gets Federer through.

Image source, Getty Images

Don't forget, before this tournament, Federer had not played any competitive tennis since Wimbledon in the summer.

He's now on his way to beating the world number five and reaching the quarter-finals of a Grand Slam, at the age of 35.

Imagine that in any other profession?

Let's say I'm a milkman and I take six months out. I haven't moved a single bottle of milk in competitive action for half a year.

There would be a lot people not getting their milk on time in my first run back on shift.

Anyway, I'm thirsty.

Image source, EPA

Oh boy. The world number five is being made to look like a child by the master.

Everything is coming back and a Federer forehand can only be prodded back into the net from Nishikori for the break and the set.

Nishikori is in the eye of a Swiss storm right now.

The Japanese is being hit to the left, to the right, back again. The court looks like an airport runway for Federer right now as he just unleashes it into the gaps.

Double break up for Super Roger.

Nishikori is tentative and indecisive and it's the invitation the Swiss needs to sense a killer blow is a foot.

Nuren: How does Federer do this? At 35, after 6 months absence.

Kushal: Don't want Federer or Nadal to win. Rooting for Wawrinka! 

The gears have got stuck a bit.

A double fault from Federer is followed up by a powerful ace, and then another double fault from Federer has him shaking his head.

He saves a break point with a superb drop shot that leads to an overhead smash and muscles through.

That may have been Nishikori's chance.

You feel Federer is slipping through the gears here.

He gives himself three break points, squanders two, but emerges triumphant from an emphatic rally.

Image source, AP

Just joining us after a heavy night? It probably wasn't as bad as Andy Murray's.

The world number one is out of the Australian Open after losing 7-5 5-7 6-2 6-4 to German 50th seed Mischa Zverev.

Read more here.

And British interest in the men's draw as Dan Evans' heroics are ended by Jo-Wilfried Tsonga.

Read more here.

Nishikori tries to mix things up by standing deep of the baseline on the service return.

Federer is unruffled, for the most part, as he takes a hold to 30.

Nishikori steadies the ship and holds well to kick off the third set.

Federer dropped just four points on his serve in that set.

Formidable stuff.

Image source, EPA