Russell Fuller
BBC tennis correspondent at Melbourne Park

ESPN have just reported that Simona Halep went into hospital overnight for four hours and was treated for dehydration.

We hope she makes a speedy recovery but it does put another slant on things.

Why I'm uncomfortable with roof being closed it because it's so borderline. The roof hasn't been closed in the first week so why do it for the final?

They were obviously in possession of this information about Halep and the conditions are little bit too brutal.

I would like a slight revision of the rules. Roger Federer doesn't run this tournament but he has had the best of the conditions. He plays the night session in every match so it's not a completely level playing field.

Federer holds!

Marin Cilic's chance goes begging as he drifts another backhand wide.

Image source, AFP

The Croat attacks the Federer serve, but pops a backhand into the net, and then he goes long.

Advantage Federer.

Image source, EPA

A whipping, curling ace from Roger Federer down the T that just flirts with the line, beautiful.

But now Cilic has set point...

Double fault from the defending champion, who is serving to stay in the second set.

The crowd is getting a little edgy, Federer just takes a moment to compose himself, but it's Cilic who rallies to 15-30.

Well, Marin certainly does!

Image source, Reuters

Cilic snaps down a mammoth first serve to take advantage, and then opens up his body to slam a forehand winner into the space vacated by Federer.

He holds, and is one game away from the second set.

A second serve ace from Marin Cilic to save break point - brave as you like!

Image source, Reuters

We've seen the magic from Roger Federer, now he's showing a bit of the grind.

The Swiss keeps himself in the point at full stretch and then pulls out a fantastic backhand winner.

Break point.

We've just seen a smart catch from one of the court-side ballboys, be taking wickets in Ashes series of the future no doubt...

Roger Federer gets the upper hand on Marin Cilic's service game, and the salmon-sneakered Swiss then screeches across the Rod Laver Arena surface to spin a backhand down the line.

Hawk-Eye says it's just out, that was nearly sublime!

30-15.

Image source, Getty Images

Pat Cash
Former Wimbledon champion on BBC Radio 5 live

Federer's depth today has been exceptional. He's hitting the baseline and keeping Cilic off balance.

Andrew Butler: I've only just discovered that Roger Federer has TWO sets of twins, which seems like the most Roger Federer thing ever.

Here are his identical twin daughters Myla and Charlene, aged eight, pictured at Melbourne a couple of years ago. He's also got identical three-year-old twin sons Leo and Lenny.

Image source, Getty Images

Roger Federer not looking quite as relaxed as he was in the first set, serving his first double fault of the game.

I speak too soon... he responds with a perfectly-placed ace. And then holds.

Smart backhand passing shot from deep from Cilic, catching Federer at the net and it drops off the Swiss' strings to the floor.

He goes long off the next exchange, and that's 15-15.

Cilic polishes off his service game with an ace, his seventh of the match.

Image source, AFP

Cilic has found form on his serve, but Federer attacks after the Croat's first effort goes astray and the sixth seed can't find the line with a crosscourt backhand.

The next, first serve, is huge, a right wrist-rattler, and he leads 40-15.

Russell Fuller
BBC tennis correspondent at Melbourne Park

Very marginal call to close the roof - during the warm up the humidity/heat index used was either at, or just 0.1 points above, the threshold which can trigger the extreme heat rule.

Image source, EPA

Apparently this match is being played indoors due to the "wet bulb globe temperature...", or something like that.

Think I'll stick to the tennis.

Roger Federer cruises into a 30-0 lead with a well-taken volley on the run, and then wraps a punchy serve in followed by an ace for a rapid hold.

Image source, AFP

Piers Newbery
BBC Sport at Melbourne Park

It’s always remarkable and impressive just how quickly spectators can complete a refuelling mission at a tennis changeover. There is extra incentive tonight as it remains pretty sticky under the roof.

The Croatian fans are just starting to make their voices heard now as their man gets a foothold in the match - although a very local sounding “Yeah mate!!!” greets his latest hold - and a bit of Federer defensive magic, swatting back smashes, gets the many Swiss flags fluttering.

Image source, Getty Images

Cilic cracks another one of those trademark serves towards his opponent, Federer can't deal with it.

The next one is also too hot to handle.

Cilic follows up with an ace. An important hold.