Djokovic entered Sunday’s final tied with Roger Federer on six titles at the season-ending tournament for the year’s top eight players.
And he stretched out his arms and beamed broadly after clinching his seventh when Sinner double-faulted.
The victory had echoes of the clinical way Djokovic dispatched second-ranked Carlos Alcaraz in Saturday’s semifinal encounter.
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“I’m very proud of the performances these last two days against Alcaraz and Sinner, probably the best two players in the world next to me and Medvedev at the moment, and the way they have been playing I had to step it up,” Djokovic said.
“I had to win the matches and not wait for them to hand me the victory and that’s what I’ve done. I think I tactically played different today than I have in the group stage against Jannik, and just overall it was a phenomenal week.”
It was his fourth win over Sinner, who had recorded a first-ever victory against Djokovic in the group stage in Turin and was the first Italian to reach the final.
But Djokovic was in imperious form on Sunday and won 14 straight points from the end of the first set to the third game of the second to leave him firmly in control and subdue the Turin crowd.
Djokovic had already secured the year-end No. 1 ranking for a record-extending eighth time by winning his opening match at the ATP Finals.
After this tournament, Djokovic will become the first player to hold the No. 1 ranking for 400 weeks, with Roger Federer at 310 the only other man to eclipse the 300-week mark.
It was also only the second time in the last 15 years that a player has made the finals of all four Grand Slam tournaments and the ATP Finals. The only previous occasion was when Djokovic did it in 2015