Image source, Reuters

Marin Cilic is really not happy about that time violation and is chattering away to the chair umpire all through the drinks break.

He's wound up and back up on the court - and he's got a 0-30 lead.

The Croat nets and then hits long as Nadal levels the score.

Then we go to deuce again...

David Law
Radio 5 live sports extra commentator at Melbourne Park

Image source, Reuters

I don't think I've ever seen Marin Cilic lose his temper but I think he might lose his rag here.

Oh, Rafa. Stop that. Stop that now.

The world number one, sends a stinging forehand winner down the line to bring up two break points. That is so ridiculously good.

Cilic is then called for a time violation which he is not happy about one bit. The Croat is muttering away to himself.

And then he lands a double fault. Ouch. Nadal breaks.

Nadal rocks out the serve-and-volley to bring up another advantage and Cilic goes long.

The world number one holds...just.

*denotes next server

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Another Aussie sports star is in the house - cyclist Cadel Evans. Those seats look posh - cinemaesque.

Image source, Getty Images

Nadal's been given a stern test now on his own serve, as Marin Cilic brings up a single break point.

It goes amiss as Cilic skies the ball up and over. Rafa allows himself a left-hand pump and curl of the bicep for that.

The Spaniard takes the advantage but can only plant into the bottom of the net on the next point. Deuce number two.

The crowd are very impressed by a Rafael Nadal backhand which sinks deep into the blue court. It brings him a break point, which is immediately saved by a smash down from Cilic.

A big ace - at just under 130mph - from the Croat gives him the advantage and then Nadal overcooks past the baseline.

A brave hold from Cilic.

Image source, EPA

Amazing, amazing spot by the Aussie Open social media team., external

The world number one, who is super super superstitious, never hands his towel back to the ball kids until he's hopped over every letter of the word 'Melbourne' which is printed on the court.

Remarkable!

It obviously works - Nadal holds to love.

Well done that man. Marin Cilic rises off the ground to hit a huge backhand past his opponent for 30-15.

Nadal then mucks up at the net, and Cilic finds a big forehand to hold.

Australia cricket captain Steve Smith is watching on from the stands. His side regained the Ashes but they're currently 3-0 down in the one-day series against England.

Maybe Rafa can offer some advice...

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Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

There's 52 minutes on the clock which, for a 6-3, is a pretty long set. The exchanges have been pretty tough and there have been some long service games. It's been a pretty even match but Rafa, when he's needed to, has found the serves he required and stepped up.

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Set point number two comes Nadal's way. Saved again by a graceful yet effective backhand from Cilic, who's got his groove back.

The Croat smacks long and hands over a third set point.

Rafa takes it with a trademark whipped winner. That wasn't as easy as the scoreboard might suggest - 54 minutes!

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

Cilic is actually playing well on the ground strokes. He's really good with his footwork and his preparation, and he generates some power. He is capable of hitting through Rafa.

Cilic isn't lying down here - a forehand winner cross-court gives brings him level at 30-30.

But Rafa's not having it. Not for one minute. He's got a set point.

Not for long, mind. A rapid winner on the line takes us to deuce. Here we go again...

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

You knew Cilic was in trouble when he came up to the net, and Rafa just ripped the ball past him. If you're going to commit against Rafa Nadal, you better come in with some serious quality.

Cilic cranks a forehand way, way over the baseline and goes 0-30 down, and Rafael Nadal brings up three break points with a beauty of a backhand straight down the court.

Cilic saves one with an ace. Or did he? Rafa is challenging...but it's on the line.

Then the Croat forces the ball over the tramline. We have our first break - and it goes to the world number one. He's going to serve for the set.

Rachel T: Hoping this is a five hour, five set marathon so that the winner is nicely exhausted.

I don't - I'm typing with a broken finger after an unfortunate netball incident.

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

I love seeing Rafa Nadal up at the net. He is so clinical. He never has to defend, you don't see him lunge - he just picks his moment perfectly.

On the second deuce, Rafa Nadal comes into the net to plant the ball past his opponent to take the advantage, before going on to hold his serve again.

This is going to be a big ol' battle.

Cilic is fist-pumping as he comes out on top of a decent rally with a 96 mph winner. He's looking confident and riled up.

Meanwhile, Nadal is looking a tad rattled, which isn't like him. He double faults to take us to deuce.

The world number one slaps the net on the next point and hands Cilic his first break opportunity.

It's saved instantly with a huge ace! Deuce.