But it is not a problem for Murray, who takes the two points to hold.

If Murray breaks in the next game, he will be the Paris Masters champion.

Let's see what he has got...

Deuce in the third set at 4-4. This is now a hugely important game...

Andy Murray is doing his best to give John Isner a helping hand with a double fault.

An excellent exchange in a rally between the pair sees Isner rattle the net, before passing with a forehand to the left. How Isner continued to keep that rally going after having the ball aimed at his nose I will not know.

Anyway, Murray is starting to get a little sloppy, seeing a forehand hit the net and go wide.

Murray leads 40-30, but a booming return from Isner doesn't give his opponent a chance and we go to deuce.

Arthur Clarke: The number of aces from tall players is so boring. Never mind talk of shortening the service box, just ban anyone over 6'2. Easy.

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Not for the first time, Isner sends a backhand volley sailing out of the court, he really should be doing much better.

But when you have a big, booming serve in your armoury, it's no problem.

Not one, but two consecutive perfect serves. Too good and Isner levels.

The match ticks over the two hour mark.

Isner is not giving an inch and looks like putting a dampener on Murray ascent to the top of the world.

However, an ace sees the Scot move to 40-0, and he wins the game as Isner's volley strikes the net.

More of those quick games needed for Muzza.

Murray makes Isner scramble with a lobbed return and the American looks to be in a bit of a pickle, but gets some good luck as the ball flicks the net to land in the court.

Oops, once again Isner with a return which goes over via the top of the net and he says sorry.

Murray doing his best to keep his cool, not easy when it feels like the whole world is against you.

Murray goes long and Isner closes out the game.

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Twit553019: C'mon Andy!! You got this 

Marie Smith: It's typical for Murray to tease us with a deciding set - life as a Murray fan never straightforward - that's why we love him! 

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Isner wants to continue attacking with some deep returns, but he needs to take a bit of weight off them as they are sailing out of play.

Murray whizzes through the game with some quick serving to edge ahead again.

Having been made to do the running, Murray now needs to give Isner some of his own medicine.

Big John is not looking too mobile as Murray sprints into the net to pop over backhand winner.

Isner goes wide and Murray has break point at 30-40. Can he convert it? Nah, a rocket of an ace from Isner for deuce.

Have some of that, Andrew. Another ace from Isner, before Murray replies to a big serve, but it's easy for Isner to close out the game.

If in trouble, pull out the big serves.

The two players take a break and John Isner has called for the physio.

He is having his knee massaged. It is one of the biggest knees I have ever seen, the size of it!

The physio can barely cover it despite using both hands to apply some ointment.

Isner hobbles back on and will serve.

A rare long rally between the two is won by Murray, who forces Isner to slice into the middle of the net, before a backhand goes long. 40-0 Muzza and he closes out the game without any problem.

Isner again making Murray do all the running and passes him with a winner to the left.

Murray then puts Isner's serve into the net and the big USA man holds, having been in a spot of bother.

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Isner on serve with a bad start, a horrible hoick out of the court, but he pulls himself together with a nice passing winner from the net.

The American is making Murray dance here, volleying backhand which lands a foot inside the court - Murray screams to himself in anger.

It looks to have put Isner off as a backhand volley sails wide for 30-30. Tight.

Isner at the net again...but a drop volley is WIDE.

30-40 Murray, can he break?? No. Isner passes Murray for deuce.

Katie: Come on Andy!!! really thought it wouldn't have to go to three sets

Alex Shcnopple: Fantastic afternoon, 13 goals (to date) in Premier League & there's brilliant on court effort in #bbctennis, external c'moooon Utd & Andy Murray :) 

Andrew Green: Murray all the way!

So it's Murray to serve first in the third and final set.

Isner has changed from a white to a red shirt. Big mistake, the white one was bringing him good fortune, this one may not do the same.

Anyway, a couple of mistakes from both players leaves the game nicely poised at 30-30 and Murray cannot afford to make another mistake.

He doesn't as his next serve is too good for Isner, before the American clips a backhand into the net.

"COME ON," shouts Murray to himself.

Well that wasn't in the script. Can Isner go full party-pooper, or will Murray turn it on in the third set to celebrate his ascent to world number one in style?

Image source, Getty Images