LONDON -- In the 10 years that London has staged the season-ending ATP Finals -- the event for the year's eight top players -- Novak Djokovic and Roger Federer have been about as dominant as it's possible to imagine.
Although Russian Nikolay Davydenko won the title in its first year in the English capital, at least one of Djokovic and Federer has made the final in all but one of the other nine years, with the pair facing off in the title match against each other on three occasions.
This is the 11th and penultimate year in London -- the finals will move to Turin, Italy in 2021 -- but the tournament has a fresher feel than normal, thanks to the presence of four players age 23 or under.
At 22, Alexander Zverev is back to defend the title he won 12 months ago, Daniil Medvedev (23), Stefanos Tsitsipas (21) and Matteo Berrettini (23) have all qualified for the first time. Even Dominic Thiem is still relatively fresh-faced, in tennis terms, at 26.
"I believe the competition between us is something really important for the sport," Tsitsipas said on Friday. "We are all young, we're just getting started, so we all want to beat one another. But we appreciate each one's game, each one plays differently, and it's quite interesting to see so many varieties.
"I mean, we are the future, we are the ones who [will be] filling the stadiums, and we're also going to create the future for our sport, together with other younger players."
As the eight men gathered for their pre-tournament commitments on Friday, taking a boat ride from the London Eye to the tournament venue at the O2 in southeast London, the youngsters contrasted neatly with the old guard of 38-year-old Federer, 33-year-old Nadal and 32-year-old Djokovic.
And compared to the previous generation, from which only Juan Martin del Potro and Marin Cilic won Grand Slam titles, this group of youngsters seems to be a cut above, a feeling not lost on Djokovic, Nadal and Federer.
"What I like about the young guys like Matteo here qualifying for the first time, it goes away from just saying like: 'Oh, we have some talented players on the tour,'" Federer told reporters.
"There's a difference between that and being something of a national hero in your own country already, being a top-10 player in the world in tennis, which is not easy to achieve.
"I think that's great that they're part of the finals. It's going to give them great experience as well moving forward to achieve things at Slam level, Masters 1000, being surrounded with the eight, having the pressure of playing against fellow top-10 players from the get-go here.
"It's something that will only help your career. Sascha's [Zverev] win last year was definitely a bit of a catalyst for the rest of the group who have qualified this year."
Djokovic, who would equal Federer's six ATP Finals victories if he wins this week, believes the rivalry between the new brood will help them as they try to take over at the top.
"I think it's a great message for the sport," he said. "It was inevitable that it was going to happen, that we were going to have a really successful next generation coming in.
"I think Roger, Rafa and I are still glad that we're in the mix. That's not going to carry on forever. So I think the sport is in good hands."
Nadal has never won the season-ending title and has pulled out through injuries on six of the 15 occasions he has qualified, as well as withdrawing after one match in 2017.
Struggling with an abdominal strain he picked up during last week's Paris Masters, he is optimistic that he will be fit this time. At "33 and a half" he admits he is "old to play tennis but young as a human," and knows that winning the title for the first time will be a huge task, not least because of the youngsters.
"I think they're super-good -- they say they're the future of our sport, but they're the present," Nadal said. "They have good competition between each other in front for the next years. They're going to fight for the same things, they have more or less the same age, so it's going to be good rivalries for our sport. I will be happy to keep competing with them for a while, and then I will be happy to watch it on TV."
All four of the youngsters earned their places in London. Medvedev reached the US Open final and reached six straight tour finals. Tsitsipas won two ATP titles and made the semis of the Australian Open. Zverev recovered from a poor first half of the year to qualify for London, and Berrettini made the semis of the US Open and picked up two titles to become the first Italian to qualify for the season-ending finals since Corrado Barazzutti in 1978.
Their only problem is that the old guard are still there. Nadal and Djokovic won two Grand Slams apiece in 2019 and are battling it out to end the year ranked No. 1, while Federer, who turned 38 in August, was just one point from another Wimbledon title and won four more tournaments.
When Federer's career tally of 103 titles was mentioned on the boat, Berrettini and Thiem looked at each other and just laughed. Nadal, Djokovic and Federer are likely to take some beating once again.
"I think the next two, three years will be very exciting," Zverev said. "But the other guys are still there, they're still playing the best tennis in the world, they're still better than us, because they're the ones winning the biggest tournaments. But I think the young guys are improving quite quickly."