Andy Murray beat Milos Raonic in a gripping semi-final to reach Sunday’s final of the ATP World Tour Finals.

The Briton, 29, triumphed 5-7 7-6 (7-5) 7-6 (11-9) in three hours and 38 minutes to reach his first season-ending final in London.

He will face Serbia’s Novak Djokovic with the winner finishing as year-end world number one.

It is the first time the battle for the top spot has been fought in the final match of the season.

Murray’s earlier victory over Canadian fourth seed Raonic extended the Scot’s winning streak to a career-best 23 matches, stretching back to September.

It was Murray’s second lengthy encounter in four days, breaking the tournament record of three hours and 20 minutes he took to beat Japan’s Nishikori in the round-robin stage on Wednesday.

“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.”

Murray was yelling at himself and 17,000 spectators were screaming with every twist and turn before he finally prevailed in an extraordinary contest.

He twice failed to serve out the match as the clock ticked past three hours in the final set, and three match points then slipped by in the tie-break.

Raonic had lost his past seven matches against Murray, including the finals at Queen’s Club and Wimbledon this year, but when his chance came with a match point of his own it was snuffed out by a sharp Murray volley.

Finally, at the fourth time of asking, Murray converted a match point to reach his first final at the O2 Arena and remain in control of his number one hopes.

“It was an amazing atmosphere,” added Murray.

“The longer the match went on, the louder the crowd got. This is what we play for. Matches like this and arenas like this. This is one of hardest matches I’ve played indoors.”