Miles Maclagan
Former British Davis Cup player on Radio 5 live sports extra

Image source, Getty Images

There's a bit of tension out there and Cilic is looking dangerous right now.

Cilic again comes out on top in a rally when Murray makes another unforced error from the baseline. It's 15-30.

Murray then introduces backhand slice in the middle of the next rally which baffles Cilic. 30s each.

Matters become a touch fractious when Murray quizzes the umpire about what seems to be an issue over Cilic talking to the umpire. Hmm.

Murray all of a sudden faces break point - a loss of concentration?

He gets out of the hole with an ace before Cilic makes an error with a long forehand. Or was it? He didn't challenge and the ball was shown to have actually landed on the line.

Yikes!

It's been a punishing season for both players. Both look, understandably, a little fatigued.

Cilic actually wins a rally and then goes on to win his service game after Murray's return is a tad bit too long. The Scot looks to the umpire to semi-question it. But he knew really.

Miles Maclagan
Former British Davis Cup player on Radio 5 live sports extra

Murray has such confidence after winning so many matches and titles and also by being world number one. It wasn't a spectacular set of tennis but it's a very big arena and it can take a little bit of getting used to.

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Murray has a lot of artillery but one of his key strengths is outlasting his opponent in a rally.

Doing just that forces an error from Cilic as the Croat fires his forehand return into the net. The man with the dazzling shorts then fails to deal with a heavy serve out wide.

Murray - not at his best so far - takes the first set.

That took 46 minutes.

Ahh yes, GB diving legend Tom Daley's also in the O2 crowd. I'm surprised he's not tried to dive into the deep blue court. Admittedly, that would be painful.

Cilic wins his service game to love. I think Murray was saving his energies for the next game.

Miles Maclagan
Former British Davis Cup player on Radio 5 live sports extra

Murray put a few miles on his legs in those last two games. He's been forced into it by Cilic's aggressive hitting.

So which VIPs have we got in the crowd tonight:

Speaker of the House of Commons John Bercow and ex-England skipper Alec Stewart.

They're the ones I've seen so far.

Back to the tennis. Cilic should have made it 15-30 but his rash forehand at the net clips the cord and flies out.

The pair then exchange errors before Murray's successful serve and volley tactic and a long return by Cilic sees the Scot hold again. Just.

Miles Maclagan
Former British Davis Cup player on Radio 5 live sports extra

Image source, Getty Images

Murray is getting everything back and that is making Cilic push harder and harder and bringing more and more mistakes.

Murray finally shows a glimpse of his ability to stretch players around the court - even 6ft 6in Cilic. He gives the Croat a good workout at 15-0 with a variety of shots before forcing an error.

However, the world number seven responds well and holds with an ace of his own.

Miles Maclagan
Former British Davis Cup player on Radio 5 live sports extra

That was such a typical Murray passage of play. Double faults, forehand errors, a bit scrappy but there he is winning the last two games.

You could write on his tombstone "he found a way".

Image source, Getty Images

Murray's first serve percentage is down at 53%. That's not great.

The world number one then makes two more double faults to take the total to four - it's now 30-40 with Murray facing another break point.

But the Scot finally produces an ace - good timing - before once again coming out on top in a rally.

He holds.

Miles Maclagan
Former British Davis Cup player on Radio 5 live sports extra

Murray is looking to take a little bit of pace off the ball. Perhaps he senses a weakness in Cilic's game when he has to force the power.

Cilic - standing at 6ft 6in - is finding his range with his serves, but his groundstrokes aren't quite up to the same standard.

A weak forehand from the baseline brings up another break point. A mid-length rally ends with another unforced error from Cilic.

It's all a bit scrappy so far.

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Those shorts Marin. The kind you'd still see on the reduced rack three months after the official end of the New Year's sales. But you know, who am I to comment on fashion.

Murray, in more understated charcoal colours, is struggling a little in his service game. 

A first double fault brings up deuce before a horribly wide angled forehand close to the net gives Cilic break point.

He takes his chance as Murray makes another error.

Break back.

Miles Maclagan
Former British Davis Cup player on Radio 5 live sports extra

Image source, PA

The quality has been very high and both players are going for it. But Murray's defence looks impregnable and other players will start to panic when they see him at the other side of the net.

Great serve and volleying by Cilic before Murray challenges again on the next point. The Croat's shot was clearly in - the replay shows that it landed full ball on the line. Two challenges lost. It remains 30-15.

But the Scot wins the next points and then outlasts Cilic in a long rally, with the Croat finishing with a wayward double-handed backhand.

It's break point. Murray takes it after Cilic fails to judge a backhand with plenty of top spin.