Stefanos Tsitsipas showed tremendous humility after becoming the youngest debut winner of the ATP Finals in 41 years.
The Greek 21-year-old, who won, 6-7 (6/8), 6-2, 7-6 (7/4) is the youngest champion since Lleyton Hewitt in 2001 and the fourth first-time champion at the event in as many years.
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Not since John McEnroe won in 1978 has a debutant claimed the title in the season-ending tournament.
It is Tsitsipas's third title of the season and comes a year after he was crowned champion at the Next Gen ATP Finals in Milan.
He has charmed the crowd at London's O2 Arena all week and earned his place in the final with an impressive straight-sets win against six-time champion Roger Federer.
The Greek star showed his class in a lovely victory speech in which he paid a beautiful tribute to his beaten rival.
"I would like to start by congratulating Dominic, you've been an inspiration not just for me but many other players around the world," Tsitsipas said.
"It's truly magnificent this fight that we put out in the centre court, I think it makes our sport great.
"It's all about this, tennis is all about this.
"Also congratulations for your amazing season this year, your team who is always supporting you, they're doing a great job. You have great chemistry guys.
"So congratulations for that and for all the hard work you're putting in this year not only but many more years to come."
Defeat is a bitter disappointment for Thiem, who won five titles this year, including the Indian Wells Masters, and reached a second successive French Open final.
The Austrian was also classy in defeat, describing Tsitsipas as "an amazing player" who "really deserves" the victory.
There was little to choose between sixth-seed Tsitsipas and Austria's world number five Thiem in the first set as a total of five break points went begging.
Both players had impressed on serve during the tournament, with Tsitsipas's figures especially striking -- 44 service games won out of 47 leading into the final.
In an inevitable tie-break Tsitsipas saved a set point at 5/6 but Thiem clinched his second set point with a powerful serve that the Greek returned into the net.
But Tsitsipas regrouped and within minutes Thiem, who beat his opponent in three sets in the Beijing final last month, was under pressure, spraying a forehand wide to concede first break of the match.
Tsitsipas held with ease and then produced a forehand down the line to break again, with Thiem threatening to unravel. Tsitsipas had won 12 out of 14 points in the set.
Thiem, who like Tsitsipas plays with a single-handed backhand, stemmed the tide but could make little impression on his opponent's serve and lost the set 6-2.
Thiem was rocking again at the start of the deciding set. He saved two break points in the first game but looked increasingly shaky and was broken to trail 1-2.
The Greek was now well on top but out of nowhere Thiem was level at 3-3 after Tsitsipas put a backhand wide.
The Austrian was now playing with much more confidence, unleashing a series of blistering winners and edged ahead 5-4 after another service hold but the rest of the set went with serve.
In the deciding set tie-break Tsitsipas took a 4-2 lead but was pegged back to 4/4.
But on the next point Tsitsipas earned a mini-break, giving him the chance to serve out for the match and he made no mistake, closing out the biggest victory of his career.
Tsitsipas has competition among his peers as the new generation attempt to dislodge Federer, Novak Djokovic and Rafael Nadal, who have dominated the men's game for the past 15 years.
World number four Daniil Medvedev won two Masters titles this year and reached the US Open final while Alexander Zverev was in London defending the title he won last year.
But Tsitsipas, who has beaten every member of the "Big Three" in 2019, will go into the new season with the belief he can take the next step towards the apex of the men's game.