Former world number one Novak Djokovic defeated second seed Stefanos Tsitsipas in two tight sets in his opening match at the ATP Finals in Turin.
The 35-year-old Serb overcame Greece’s Tsitsipas 6-4 7-6 (7-4).
Djokovic is trying to equal Roger Federer’s record of six victories in the season-ending tournament.
Earlier in the same group, Russia’s Andrei Rublev beat compatriot Daniil Medvedev 6-7 (7-9) 6-3 7-6 (9-7).
Sixth-seeded Rublev held his nerve to overcome the fourth seed after squandering seven set points in the opening set in the final-set tiebreak.
On Sunday, Rafael Nadal’s latest bid to win his first career ATP Finals title began with a loss to American eighth seed Taylor Fritz.
Top seed Nadal will face Canada’s Felix Auger Eliasime in his second round-robin match of the Green Group on Tuesday.
The eight men’s players of the year are divided into two groups of four at the Turin tournament, with the top two qualifying for the semi-finals.
Meanwhile, Britain’s Neil Skopski and Dutch partner Wes Koolhoff won their first men’s doubles match 7-6 (7-3) 4-6 10-5 against Australian pair Nick Kyrgios and Thanasi Kokinakis.
The pair have enjoyed incredible success in their first year together, winning seven titles including Masters 1000 victories in Madrid, Montreal and Paris, and ending 2022 as the year-end world number one. .
Former world number one Joe Salisbury, tied for second with American Rajeev Ram, will take on fellow Brit Lloyd Glasspool and his Finnish partner Harri Halivaara on Tuesday.
