Alexander Zverev dominated Daniil Medvedev in Turin to win his second ATP Finals title.
The German world number three avenged his loss to the Russian second seed in the group stage with a 6-4 6-4 victory.
Zverev, the 2018 champion, did not face a single break point in a serving masterclass.
“I had to play one of my best matches,” Zverev said after his sixth title of a year that included Olympic gold.
“I’m super thrilled and super happy right now. There is no better way to end the season than to win here.”
Zverev, who beat world number one Novak Djokovic on Saturday, becomes only the fourth player to beat the top two players in the world in the semi-finals and final of this prestigious tournament and the first since Andre Agassi in 1990.
The pair had already met this week in Turin, with Medvedev beating Zverev in a lengthy three-setter.
Zverev, 24, had not beaten the US Open champion for two years, losing to him five times since a victory over him at the 2019 ATP Finals in London.
But the 25-year-old Russian could not extend that winning run when the trophy was at stake as the German took an early break in both sets in a clinical display.
Zverev’s serving was almost flawless as he dropped just four points on serve in the first set and won 83% of his first-serve points. It was therefore only fitting that he sealed victory with an ace.
This was the first final since the tournament’s relocation from London and it was the first time since 2005 that the two finalists were aged 25 or younger.