Novak Djokovic defeated Norway's Casper Ruud 7-5, 6-3 to collect a record-equalling sixth ATP Finals title on Sunday, earning the biggest pay cheque ever in tennis — $US4,740,300 ($7,109,454) — for completing the season-ending tournament unbeaten.

In front of a rapturous crowd in Turin, Italy, Djokovic sealed victory in style with his ninth ace to collect the series title for the first time since 2015.

"Got to stay focused the entire match, every single point, the momentum can switch to the other side really quickly," the Serbian said in a televised interview after the match.

"The fact that I waited seven years makes this victory even sweeter," he added as he matched Roger Federer's haul of six titles in the season-ending event.

Ruud, 23, has enjoyed the best tennis of his career in 2022 and battled toe-to-toe with the 21-times major winner early on but produced two clumsy errors to hand Djokovic the break at the end of the first set.

Djokovic put his foot on the accelerator from there on, harnessing his mighty forehand to break Ruud in the fourth game of the second set.

The Norwegian threw everything he had at the veteran in a 36-shot penultimate rally but the Wimbledon champion was simply too sharp, outlasting his opponent in the marathon exchange and holding his arms out wide after clinching the title.

Djokovic, at 35, is the oldest to win the title, ending the season on a high note after a year of ups and downs.

He was unable to defend his title at the Australian Open in January  because he was deported from Australia due to his refusal to be vaccinated against COVID-19.