LONDON • Three years ago, Stefanos Tsitsipas arrived in London as a wide-eyed teenager, happy to offer his services as a hitting partner for Dominic Thiem, whom he knew a little.
A year ago, he won the Next Gen Finals, the showcase tournament for players 21 and younger that is meant to be a harbinger of future greatness in men's tennis.
In his case, the future is now.
In an up-and-down final on Sunday night, he got to know Thiem a lot better, rallying and holding on to beat the fourth-ranked Austrian 6-7 (6-8), 6-2, 7-6 (7-4) to win the ATP Finals, the most significant title of his burgeoning career, on his competition debut.
At 21 years and three months, Tsitsipas is the youngest champion of the season finale since Australia's Lleyton Hewitt won it in 2001.
"Holding this trophy feels amazing, just unbelievable," the Greek, who yesterday finished the year as world No. 6, said. "I've never received so much support in my life.
"I was excited to be part of the Finals experience. For me, it was already a big thing. Now that I'm a champion, I don't know how to explain it. I honestly don't feel anything, because it's too many emotions to feel something."
Tsitsipas is the fourth first-time champion here in a row, following Andy Murray, Grigor Dimitrov and Alexander Zverev.
While the quality has sometimes dipped over the years, given the event's place at the end of the calendar, last week provided rich entertainment on nearly every day, as well as a couple of surprises.
It was a reasonable expectation that at least one of the Big Three in Roger Federer, Rafael Nadal and Novak Djokovic would contest the title, but they succumbed to the workload and the excellence of their younger opponents.
World No. 2 Djokovic will almost certainly be back next year but there is no certainty that top-ranked Nadal will get to the line, given his injury problems, or world No. 3 Federer, who will be 39 then.
Youth, meanwhile, is prospering although Tsitsipas acknowledged the fact that, despite all the razzmatazz surrounding the ATP Finals, it is the Majors that are the true yardstick in tennis.
He said: "I believe I'm really close to being crowned a Grand Slam champion. I know these are strong words that I say, but I do feel I belong there."
The best-of-five set format at the Majors, however, plays into the experienced hands of the Big Three, who have collected an astonishing 55 out of the 66 titles on offer since Wimbledon in 2003.
Tsitsipas, whose semi-final appearance at this year's Australian Open remains the furthest he has progressed at a Slam, admitted that the new wave, including French Open finalist Thiem, Zverev and US Open finalist Daniil Medvedev, might have to play the waiting game just a bit longer.
Asked when they would finally make the breakthrough, he said: "For the young guys, it's all about time. I don't know. We will have to beat them (the Big Three) or wait for them (to retire)."
THE GUARDIAN, AGENCE FRANCE-PRESSE, NY TIMES