Stefanos Tsitsipas on Sunday became the first Greek to win the ATP Finals by defeating Austria's Dominic Thiem 6-7(6), 6-2 and 7-6(4).
Tsitsipas established another milestone by - at age 21 years, three months - becoming the youngest player to win the tourney since Australia's Lleyton Hewitt triumphed in 2001 in Sydney at age 20.
The Athens native, who won the New Generation ATP Finals last year in Milan and lost only one match during the tourney (to Spain's Rafael Nadal during the group phase), recovered vigorously after losing the first set on a tiebreak, ultimately defeating Thiem in two hours and 35 minutes.
Although he was having symptoms of cramps late in the match, Tsitsipas still managed to pocket the most important title of his career so far.
Although he took the first set, Thiem then lost the first four games of the second set, winning only one point during that time, a situation from which he never recovered.
In the final set, although Tsitsipas went up by 3-1 at first, Thiem battled back and made it a contest, although he ultimately went down to defeat in a second tiebreak.
Americans John McEnroe (at 19 years, 11 months), Pete Sampras (20 years, three months) and Andre Agassi (20 years, three months), as well as Germany's Boris Becker (21 years, 13 days), have been the youngest players to win the title, but no American has managed to win the ATP Finals for 20 years, since Sampras triumphed in Hannover, Germany.
Tsitsipas, who is now ranked No. 5 in the world, already has won four titles - three of them garnered this year at Marseilles, France; Estoril, Portugal; and London - and he has won three of them on covered courts.
Tsitsipas pocketed a check for $2.65 million for the tourney win on Sunday night, along with 1,300 ATP ranking points.
He had played Thiem twice before in Grand Slam finals - both at Roland Garros, in 2018 and 2019.
Despite the loss, Thiem will rise one slot in the world rankings, now sitting at No. 4.
This is the fourth consecutive year in which a new champion has surged forward to take the tournament after the victories of Britain's Andy Murray in 2016, Bulgaria's Grigor Dimitrov in 2017 and Germany's Alexander Zverev last year.
Tsitsipas booked a spot in the championship match for the first time with a 6-3, 6-4 victory in London on Saturday over six-time champion Roger Federer.
The Greek phenom had defeated the 38-year-old world No. 3 in four close sets early this year at the Australian Open and he looked at London's O2 Arena like a player who knows he belongs on court with the veteran Swiss great.
Meanwhile, in Saturday night's second semifinal match pitting world No. 5 Thiem against world No. 7 Zverev, it was the Austrian who came out on top to book a place in the final.