A hammer of a forehand from Marin Cilic gets Roger Federer shuttling across the baseline and eventually it's too much for the Swiss to respond to.

Cilic can't coax his next effort inside the line after a fiery Federer return.

Deuce.

Image source, Reuters

Another double from Marin Cilic, he got away with a few last set but this is the business end.

Roger Federer pumps a return long and that's 30-30.

Pat Cash
Former Wimbledon champion on BBC Radio 5 live

Federer's as bad as McEnroe on these line calls!

"Let's go Roger, let's go..." is the chant ringing out around Rod Laver Arena.

Marin Cilic slaps down a popping second serve that Roger Federer can only lash into the net, and the Swiss isn't happy with the line judge...

Image source, Reuters

William Tomaney: Can’t stand how pro Federer the crowds always are. It’s nice to see someone take a game to him for once. Would they rather have a 3-0 walkover with the opponent offering nothing?

Image source, Getty Images

That's not the Roger Federer we're used to - roaring after winning a point and thrusting both hands out in front of him.

But that's what this final means, and how far Marin Cilic has pushed him.

The defending champion claws back to hold with a wonderful passing winner off his backhand.

Image source, Getty Images

Pat Cash
Former Wimbledon champion on BBC Radio 5 live

I'm wondering if Cilic has the mental capacity to finish this off.

Federer saves, as Marin Cilic can't pull a return high enough to clear the net.

But the Swiss then drops a slice long and it's a second break point chance for the Croat.

Image source, EPA

Great defence from Roger Federer, stretching to clip a forehand just over the tape, but Cilic flies into the net and cracks a volleyed winner beyond the second seed.

Federer punches a backhand into the net, that's break point.

Marin Cilic is looking cool, calm and collected - he pulls back to 30-30, before thumping a forehand wide.

Piers Newbery
BBC Sport at Melbourne Park

An amazing turnaround from Cilic, who is finally playing the sort of aggressive, bullying tennis that took him to the 2014 US Open title (and is totally at odds with his very friendly personality).

Federer helped him out by making just 36% of his first serves in that fourth set, allowing the Croat to tee off on the second-serve returns.

Image source, AFP

Pat Cash
Former Wimbledon champion on BBC Radio 5 live

I don't know if he can keep it up but he's winning all the long rallies at the moment. It's something we've seen since the end of the last set.

Well, it's a pretty impressive locker Roger Federer boasts, and he rattles to 30-0 before Marin Cilic engages the Swiss and gets the better of the rally.

This is new territory for Roger Federer in terms of the 2018 Australian Open, he glided through to the final without dropping a set.

What's the 36-year-old got left in his locker? Two hours, 33 minutes gone...

Joel Newnham: This final set will either be 6-1 or 9-7.

Michael Rose: Two sets all. Well done @cilic_marin. This is now a classic final.

Gigi Salmon
Radio 5 live commentator at Melbourne Park

Who would have thought after a 24-minute first set we would be going to distance?

George Meixner: I've been enjoying the comms all week, but why does all the sport in Oz happen at the same time? #bbctennis , external@bbctms, external

Sorry about that. If it helps, we don't know which timezone we are in here at BBC Sport...

Marin Cilic takes the fourth set! The Croat is in superb form right now.

A fifth set awaits...

A mammoth serve. Three set points.