Stefanos Tsitsipas became the youngest ATP Finals champion in 18 years after battling back from a set down to beat Dominic Thiem in a thriller at London's O2 on Sunday.
Appropriately, the two standout performers clashed in the final after 21-year-old Greek debutant Tsitsipas eclipsed six-time champion Roger Federer and Austrian Thiem dispatched defending champion Alexander Zverev.
The first-time finalists' technicolour games lit up the O2 Arena as the tournament reached its climax with Tsitsipas looking to become the youngest winner of the tournament since a 20-year-old Lleyton Hewitt was victorious in 2001.
He is the youngest debutant to lift the trophy since John McEnroe back in 1978, while Thiem was aiming to win his sixth ATP title of 2019.
They were eventually separated by a tiebreak in which Tsitsipas saved one set point but the fifth seed from Austrian sunk his second opportunity with a devilish first serve after 65 minutes of intense action.
But it was Tsitsipas who sealed a sensational win 6-7 (6-8) 6-2 7-6 (7-4) at the prestigious season-ending tournament.
This was only the third time since 2002 that at least one of Federer, Rafael Nadal or Novak Djokovic have not reached the final and while it may not signal a changing of the guard, the week has felt like a momentum shift for the new generation.
While Thiem, 26, has made it through to his first final here at the fourth attempt, Tsitsipas has wowed the London crowds for the first time with his fearless attacking style.
The opening set was exhilarating as both players saved breakpoint chances in a swashbuckling opening eight games of the final - five in total - with neither man giving an inch.
Thiem's dream came to an end despite winning the opening set
Fifth-seeded Thiem was looking to extend his impressive record of 39-3 after winning the first set in 2019, but his game collapsed in alarming circumstances, and Tsitsipas, who won the ATP Next Gen Finals 12 months ago, went on to dominate proceedings to send the final into a deciding set.
Thiem, twice a French Open runner-up, has been the stand-out player all tournament despite suffering with flu-like symptoms throughout the week.
He appeared down and out when a rampant Tsitsipas broke early in the third, but a re-energised Austrian discovered a second wind to win seven straight points and move 4-3 up.
Tsitsipas sealed a memorable victory at London's O2 Arena
A nip and tuck conclusion to the final was settled in a tiebreak situation for just the third time in the tournament's history.
Thiem looked down and out at 4-1 down but he quickly levelled only to lose concentration when his backhand return sailed long.
Tsitsipas grasped his opportunity and kept his nerve to win the biggest title of his career after two hours and 36 minutes of breathtaking tennis.