Andy Murray battled past Milos Raonic to reach the ATP World Tour Finals showpiece match ©Getty Images

Andy Murray and Novak Djokovic will square off in the final of the Association of Tennis Professionals (ATP) World Tour Finals at the O2 in London tomorrow where the world number one spot will be on the line as well as the title.

Britain's Murray overtook Serbian Djokovic at the top of the world rankings earlier this month but he knew he needed to match his rival's performance at this tournament in order to stay there.

It means there will be plenty at stake when the two heavyweights collide in what should be a mouthwatering showpiece match.

Murray, the back-to-back Olympic champion, won an epic semi-final against Canada's Milos Raonic today, the same player he beat to win his second title at Wimbledon this year.

The Scot eventually came through 5-7, 7-6, 7-6 to reach the final of the season-ending event - which only invites the top eight players in the rankings - for the first time. 

In the first set Murray was uncharacteristically error-prone and at 6-5 behind he conceded three set points.

After saving two, he sent the ball crashing into the net as the Canadian drew first blood.

It looked like Murray was heading out of the tournament when Raonic opened up a 2-0 advantage in the second set, but he broke back to love before going on to level the match 7-5 in the tiebreak.

In the final set, Murray was twice unable to serve out the match and he squandered three match points in the second tiebreak.

Novak Djokovic brushed aside Kei Nishikori ©Getty Images
Novak Djokovic brushed aside Kei Nishikori ©Getty Images

Raonic earned a match point of his own but a Murray volley kept the game going.

The Briton was then eventually able to come through 11-9, in the longest-ever ATP World Tour Finals match at three hours and 38 minutes.

"I didn't expect to play a long one with someone with a serve like Milos," said Murray.

"I'm tired. 

"I've played so much tennis over the last few months.  

"I'll give it my best effort - the best of what I have."

Djokovic's path to the final was far more routine as he brushed aside Japan's Kei Nishikori on the hard courts, 6-1, 6-1.

"I started off very well and got a 4-0 lead," said Djokovic, the defending champion.

"I pretty much executed everything that I tactically planned to do before the match. 

"You never know how you are going to start, but I started off very well. 

"Obviously that helps when you a playing a top player."