Andy Murray and Novak Djokovic will stage a dramatic battle to finish 2016 on top of the world as the two old rivals aim for the title at the ATP Tour Finals.
A friendly rivalry that began 15 years ago when they first faced off in European junior tournaments will reach a new level over the week as they fight to end the year as the world number one.
Murray shattered Djokovic's 122-week reign at the top last weekend when the Wimbledon champion became the first British man to reach pole position in the ATP rankings.
But Murray has only a 405-point lead over Djokovic in the rankings and the Scot can be passed by the Serb if he doesn't match or better his rival's performance at the prestigious season-ending event at London's O2 Arena.
As the top two seeds, Murray and Djokovic have been drawn in different groups in the eight-player tournament, meaning they can't meet before the semi-finals.
If their 35th Tour-level meeting comes in the final, it would be a fitting occasion to decide the top ranking, which last changed hands at the Tour Finals in 2001 when Lleyton Hewitt supplanted Gustavo Kuerten.
Murray has enjoyed an incredible 11 months on and off the court in which he has won Wimbledon for the second time, claimed a second Olympic singles gold medal and become a father to baby daughter Sophia.
"This year is the best I've had on court, the last few months have been the best in terms of my consistency," Murray said.
"Away from the court it's been by far the best in my life, a big change and a great change. I've really enjoyed being a parent.
"When I step on the court I will have a little more confidence and feel better about myself.
"I don't want to spend time discussing what's happened in the last few months. I want to keep getting better.
"That's what I've always tried to do. I don't feel any different."
Although Murray has lost 24 of his clashes with Djokovic, few of his peers on the Tour question his right to be number one after such a strong year.
Djokovic agrees, saying: "I have only words of praise for what he has achieved in the last year or so.
"Definitely he is a well deserved number one at this point. He has been the best player for the last six months without a doubt.
"Whether he can sustain that is not a question for me but looking at his qualities and commitment there is a good chance he can play at this level for a long time." Djokovic has been in a slump since winning the French Open in June to complete his career Grand Slam, raising questions about his appetite for continued success.
But the 12-time major winner might find the O2 Arena is the ideal venue to restore his confidence.
He has won the Tour Finals for the last four years and another success this year would equal Roger Federer's record of six titles.
With Federer and Rafael Nadal both absent due to injury, Djokovic and Murray will be the centre of attention.
They could have very different paths to the trophy as Djokovic holds a remarkable 23-0 combined record against Milos Raonic, Gael Monfils and Dominic Thiem, who comprise his group stage opponents.
In contrast, Murray, who has never been past the semi-finals of the event, has to survive a tricky group featuring US Open champion Stan Wawrinka, as well as Japan's Kei Nishikori and Croatian Marin Cilic, who have both beaten the Scot this year.