Novak Djokovic beats Milos Raonic to make ATP World Tour Finals semi-finals

World number two Novak Djokovic saw off big-serving Milos Raonic in a pulsating contest to reach the semi-finals at the ATP World Tour Finals.

The five-time champion won 7-6 (8-6) 7-6 (7-5) at the O2 Arena to become the first man through to the last four.

The win means the Serb, who beat Dominic Thiem on Sunday, will regain the number one ranking from Briton Andy Murray if he goes on to take the title.

Raonic faces Thiem for the other semi-final place on Thursday.

Thiem beat Frenchman Gael Monfils 6-3 1-6 6-4 in Tuesday's opening match in the Ivan Lendl Group.

Murray will try to join Djokovic in the last four when he plays Japan's Kei Nishikori in the John McEnroe Group on Wednesday, a match that is live on BBC Two, online and BBC Radio 5 live sports extra at 14:00 GMT.

He has been the subject of much speculation during a relative slump in form since June, but Djokovic remains a formidable opponent at the O2 Arena.

Despite a fine performance from Raonic, the four-time defending champion made it 21 wins from his last 22 matches in east London to secure a seventh semi-final.

"Other than a couple of loose service games, I thought it was a good performance," said Djokovic.

"This definitely can serve as a great wind in the back for the matches to come."

Raonic had lost all seven of their previous matches, and won just one of 18 sets, but he hit 42 winners to 11 as he made the running for much of the two hours and 14 minutes.

Djokovic served well to save three break points in the first set and edged through a gripping tie-break when Raonic double-faulted.

The Canadian fell behind early in the second but twice recovered breaks of serve, and while the 17,000 spectators roared with every punch and counter-punch, Djokovic began to leak errors.

Raonic had a chance to level the set but snatched at a forehand, and Djokovic came through a second tight tie-break to clinch victory.

"It's just hanging in there mentally, staying strong and believing that the opportunities will arise," said Djokovic.

"When they do you have to capitalise. I think one or two points separated us today. It could have gone either way, this match."

At 23, Thiem became the youngest man since Djokovic in 2009 to win a match at the ATP finale, and the first Austrian to do so since Thomas Muster in 1996.

Monfils, 30, is also making his tournament debut but the injuries that have dogged him in the second half of the year appear to be having an effect.

The Frenchman looked to be struggling with a knee injury and was on course for a meek exit when he dropped the first set to Thiem.

A 25-minute burst of powerful hitting in the second set gave the London crowd a glimpse of Monfils at his best, but three double-faults gave Thiem the chance to clinch victory in the 10th game of the third.

Monfils will play Djokovic in his final group match on Thursday and will hope to feel the benefit of a rest day on Wednesday.

"I'll try to recover because obviously I'm not good enough to play back-to-back," he said.

* means qualified for semi-finals