A week ago, Djokovic played old rival Roger Federer, their 47th meeting, this time in the semi-finals.
Federer's first ATP Tour success came back in 2001 at an indoor tournament in Milan. He became the oldest World Number one in the 45-year history of the ATP Rankings.
Of course, in tennis years, it is long ago, but in Federer years, perhaps less so. His tournament ended in the quarters with defeat to Britain's Tim Henman.
Federer is very aware his time on the ATP Tour is limited, but has made it clear he is not thinking of retirement at the moment. Because at the Grand Slams, he could not convince again this year.
Federer turned 37 in August, with total career prize money of over $118million to his name, but he has shown no sign of stopping yet.
Ivan Lendl is third with 94 titles, while one of Federer's biggest rivals Rafael Nadal sits fourth. After scooping the Wimbledon title, Djokovic has won the Cincinnati Masters, US Open, Shanghai Masters and Paris Masters, making him the hot favourite to win the ATP Finals title.
"Everybody has a chance of beating everybody at this level". The Swiss has surprised many with his longevity and he appears to be as fit and as in form as he has ever been.
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Federer won seven titles in his dreamy 2017 comeback season.
'I grew a lot of confidence by winning a lot of matches in the last three or four months so hopefully I can have a nice season finale [in London]'.
While nobody would be foolish enough to suggest Federer will not make it past 109, Connors can breathe fairly easily for now.
If these gifted millionaires needed reminding of the world that exists outside their bubble, sharing the Friday night rush hour with Londoners - albeit in a reserved carriage, surrounded by a phalanx of aides de camp - probably is as straightforward as it gets.
I think if I won the title here, it is more about winning the World Tour Finals and not about winning my 100th. He reached the semifinals twice, in 2014 and 2016, and was beaten by Novak Djokovic both times.
The Serb has enjoyed a remarkable rise back to the top of the tennis world in 2018, becoming the first man to finish a season as world No. 1 having dropped outside the top-20 in the same year.
Federer is expected to emerge from Group Lleyton Hewitt, also featuring Kevin Anderson, Dominic Thiem and Kei Nishikori, while Djokovic is highly fancied to top Group Guga Kuerten, which also includes Alexander Zverev, Marin Cilic and John Isner.