LONDON -- A couple of days into his final ATP Finals, Chris Kermode, the outgoing CEO and chairman of the ATP Tour, was asked about his faith in the future of the sport.
"I have always [said], and I genuinely mean this, the game will carry on when Roger [Federer], Rafa [Nadal], Novak [Djokovic] and Andy [Murray] all leave the game," Kermode said.
"They have played an immense part and are obviously going to be missed, but the game will survive, and the talent that's coming through is incredible."
That talent was fully on show on Sunday when Stefanos Tsitsipas of Greece beat Austrian Dominic Thiem 6-7, 6-2, 7-6 to win the ATP Finals. Three years ago, Tsitsipas was a hitting partner for Thiem in the season-ending event. Having beaten Federer on Saturday, Tsitsipas had the crowd singing his name on Sunday. At 21, Tsitsipas' victory in his tournament debut makes him the youngest ATP Finals champion since Lleyton Hewitt in 2001. If he maintains this kind of momentum, anything is possible.
It should go without saying that any assessment of the future of the men's game should be countered by a look at the end-of-the-year ATP rankings. Nadal ended up on top for the fifth time in his career, joining Djokovic (No. 2) and Federer (No. 3) on that mark. Between them, the three men have topped the rankings 15 times in the past 16 years, and the only time one of them they didn't, the other member of the big four -- Murray -- topped the pile.
Even as they head into their mid- to late 30s -- Federer is 38, Nadal 33 and Djokovic 32 -- they have continued to dominate the biggest tournaments. Nadal and Djokovic won two Grand Slams apiece in 2019, and Federer was a point away from winning another Slam.
There have been numerous false dawns over the years. Grigor Dimitrov's win in London in 2017 might have been a catalyst for the Bulgarian to win a Grand Slam, but he struggled in the two years to follow. Alexander Zverev is in better shape, having won in London 12 months ago and then, after a tough start to 2019, qualified for the eight-man event and reached the last four.
After going out at the semifinal stage in London, Federer said it felt as if the young players were closer than ever to breaking through.
"I just think they [the Next Gen players] have proven their point this year by qualifying for the [ATP] Finals and also now at least one of them making it to the finals," Federer said.
"But then I look at the list of who finished world No. 1, who has been world No. 1 all these years, and it's just crazy that it's always one of us. But we are not getting any younger. So [the] chances [of the younger players breaking through] increase, not because we are getting worse, but because they are getting better, I believe."
When Kermode first introduced the Next Gen Finals for the top eight under-21 players in 2017, he hoped to give some of the brightest young players a bit of a spotlight to boost their profile and help tell their stories.
What the Next Gen Finals have really shown, though, is how good this generation of players seem to be. Hyeon Chung, the winner in that first year, made the semifinals of the Australian Open two months later. And had it not been for injury, he might have risen further. Tsitsipas, the 2018 winner, also made the semis in Australia and has now won the ATP Finals. Jannik Sinner, the Italian who won in 2019, could be even better than the lot.
Daniil Medvedev, the Russian, reached six finals in a row this summer, including the US Open final, while Thiem has made the final of Roland Garros in each of the past two years. Tsitsipas and Thiem have both beaten each of Nadal, Djokovic and Federer in 2019; Zverev beat Nadal in London and also owns a win over Federer this year, while Medvedev beat Djokovic twice in 2019.
Zverev, for one, believes things are about to change.
"I think next year will bring a new Grand Slam champion," he said. "We'll see who that will be, because I think the young guys are playing incredible tennis. It can be Daniil, it can be Stefanos, it can be Dominic. I'm in the mix, as well, I hope. We'll see what next year brings. But I think for the young guys, it's going to be an exciting year."
Sunday was Tsitsipas' 78th match of the year, a lot of miles on the legs for a young player. Boris Becker, the former world No. 1 and winner of six Grand Slams, believes Tsitsipas is the real deal -- if he can be smart about his schedule.
Commentating for BBC Sport, Becker said: "The secret of the success of Federer and Nadal and even Djokovic is scheduling. They know how to peak. In my opinion, the younger players play too much. But at his age, you have to play more matches to learn more. Now he's arrived, he'll have to be more careful with his schedule next year."
Tsitsipas is not short on confidence, and his self-belief, coupled with his talent and work rate, will surely carry him a long way. With Medvedev, Zverev, Thiem, Matteo Berrettini (who also qualified for London), and then the likes of Sinner, Denis Shapovalov and Felix Auger-Aliassime close behind, the next generation looks bright.
Djokovic will surely be strong again in 2020 -- Nadal, too -- and Federer is still a Grand Slam contender, as he showed at Wimbledon. But for the first time in a decade and a half, the destination of the Grand Slam titles is uncertain. Tsitsipas said he thinks he is "really close [to] being crowned a Grand Slam champion" but knows that beating Nadal, Djokovic and Federer over five sets is the biggest challenge of all.
"Someone needs ... to defeat them early rounds because once they get deep in a tournament, they tend ... to get better and play better, feel better," Tsitsipas said. "It [best-of-five sets] just gives them more chances to stay in the match. I think if things were best of three, it could have been much more different.
"They have been sharing how many Grand Slams? I don't know. Sixty-something? And for us, for the young guys, it's all about time. I don't know. We will have to beat them or wait for them."