Stefanos Tsitsipas crowned an incredible year as he battled back to beat Austrian Dominic Thiem 6-7(6) 6-2 7-6(4) to win the ATP Finals title at the O2 Arena on Sunday.

The 21-year-old debutant, the youngest of the eight qualifiers for the elite season-ender, 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.

Tsitsipas becomes the youngest winner of the tournament since Lleyton Hewitt, aged 20, won it in 2001. 

Tsitsipas said: "I was playing with nerves, it's such a big event. I was a break up in the third set, but couldn't hold it, but I'm so relieved with this outstanding performance I gave on the court.

"It's phenomenal, unbelievable to have such an army behind me, they give me energy, and belief, and I just love that.

"I would like to thank everyone who supported me with a Greek flags and made me feel at home."