ATP World Tour Finals: Novak Djokovic ready to 'fight' for number one status

Novak Djokovic has won the ATP World Tour Finals for the past four years

Novak Djokovic can take the first step towards regaining the world number one ranking when he opens his title defence at the ATP World Tour Finals on Sunday.

The Serb, 29, plays Austria's Dominic Thiem in the first of the singles matches at 14:00 GMT (live on BBC Two).

Djokovic could reclaim the top ranking from Britain's Andy Murray with another successful week at London's O2 Arena.

"It's one of the things that we're all fighting for here, let's see where it takes us," Djokovic told BBC Sport.

"Being number one in the world, in a season like this, is of course the pinnacle of the sport next to winning a Grand Slam."

The top eight singles players and doubles teams are divided into two groups of four at the ATP World Tour Finals, with the top two from each group progressing to the semi-finals.

Briton Jamie Murray and Brazil's Bruno Soares take on Treat Huey and Max Mirnyi in the evening session at 18:00, followed by Wimbledon finalist Milos Raonic against Gael Monfils.

For the first time since the season-ending finale moved to London in 2009, neither Roger Federer nor Rafael Nadal will be present as both ended their seasons early to recover from injuries.

Djokovic held all four Grand Slam titles when he won the French Open in June, but a slump in form followed, opening the door for Murray to end his 122-week stay at number one last Monday.

"Completing the career Grand Slam was of course very satisfying but it took a lot out of me emotionally," said Djokovic.

"All in all it was a great season, I'm happy about it, and I'm here in London trying to finish the season in the best possible way."

Djokovic spoke of "private issues" after he lost in the third round of Wimbledon, broke down in tears after a first-round loss at the Olympics and has had wrist and elbow injuries.

He now needs to win at least two group matches and claim a fifth successive title at the O2 Arena to ensure he ends 2016 at the top of the rankings.

"Andy deserves to be where he is," said Djokovic.

"If you look at his results in the last 10 months he's been very, very consistent, playing finals in more or less each tournament he took part in.

"You've got to give him credit for that and I'm sure he's motivated to finish off this year with a title in London."