Greece's Stefanos Tsitsipas defeats Austria's Dominic Thiem 6-7 (6/8), 6-2, 7-6 (7/4) during the men's singles final match in London on day eight of the tournament.
Stefanos Tsitsipas beat Dominic Thiem 6-7 (6/8), 6-2, 7-6 (7/4) to win the ATP Finals at London's O2 Arena on Sunday.
The Greek 21-year-old is the youngest champion since Lleyton Hewitt in 2001 and the fourth first-time champion at the season-ending event in as many years.
Tsitsipas displayed resilience and flair in equal measure to claim his biggest title to date.
Thiem edged an intense first set full of powerful baseline rallies but Tsitsipas, the first Greek player to play in the event, was undaunted and responded in style.
He surged into a 4-0 lead in the second set and Thiem appeared to be flagging when he then trailed 3-1 in the deciding set before rediscovering his early spark.
Thiem broke back to take the showpiece into a deciding tiebreak but it was Tsitsipas, the crowd favourite, who stayed strong, moving 6-4 ahead and clinching victory when Thiem fired a tired forehand wide.