World No1 Novak Djokovic starts his campaign to become the first player in 27 years to achieve a three-peat at the season finale with a potentially dangerous match against Marin Cilic.
The Serbian star is 10-0 in his head-to-head against the Croat world No9, but Djokovic was stretched to four sets in the round of 32 at Roland Garros and then survived despite being 2-1 down in the quarter-finals of Wimbledon.
Since those last two defeats, the 26-year-old Cilic has become a grand slam winner, beating Kei Nishikori to win the US Open. He did not have a good trip to China, losing early in both Beijing and Shanghai, but is coming off a victory in Moscow.
Djokovic is on the verge of a potentially historic week, and his famed mental strength is sure to see him through not just Cilic, but also the Group B.
The last man to do a three-peat was Ivan Lendl, winning three consecutive titles from 1985-87. Djokovic is also vying for a third year-end No1 ranking in four years.
The other Group B singles match, to be played earlier in the day, features Stan Wawrinka and Tomas Berdych. The world No4 Swede leads their head-to-head 9-5, and has beaten Berdych the last four times they have met.