It's been four years since the ATP announced the inaugural Next Gen ATP Finals, an event for the best under-21 players in the world.
Though Hyeon Chung of South Korea won the title, the qualifiers for the first event in 2017 included Alexander Zverev, Daniil Medvedev, Andrey Rublev, Denis Shapovalov and Karen Khachanov, while Stefanos Tsitsipas was an alternate.
On Monday, the US Open begins with five of those six players ranked in the top 10. The next generation of rising stars are not just coming, they're already here.
Andy Murray and Stan Wawrinka briefly broke the stranglehold with three Slam wins apiece but since Wawrinka won the US Open in 2016, the only win by a non-big-three player was at last year's US Open, when Dominic Thiem won his first Slam.
World No. 1 Djokovic is a strong favorite to win this year's US Open, which coincidentally would also make him the first man to win all four majors in the same year since Rod Laver in 1969. But there is a growing feeling that the passing of the baton is not too far away. Federer is 40 and facing another rehabilitation after knee surgery, while Nadal has a foot injury which will keep him out the rest of the year.
The fact that there is a group of players all around the same level is helping the pretenders believe they can finally make that Slam breakthrough.
"Probably [we] all want to be the first ones to make it," Medvedev told reporters at Flushing Meadows on the eve of the Open. "Actually Thiem is the first one, if we can call it NextGen, which we are not anymore, but we were kind of in this group, he was the first one to do it last year. Out of the big three, only Novak is here, who is of course going for the Grand Slam.
"Stefanos was in the final of Roland Garros, two sets up [on Djokovic]. I was in the final in Australia, not two sets up but still in the final. We're going to try to get (Djokovic).
"This competition to be the first one of these young guys to win a Slam ... I think everybody wants to do it."
For many years, the biggest issue always seemed to be that to win a Grand Slam, the chances were that a young player would have to beat at least one, and sometimes two of the big three to win a major title.
Wawrinka did it in 2014 when he won the Australian Open and at Roland-Garros in 2015, but the younger players have fallen short so far, sometimes managing a big victory but then finding another roadblock in their way.
Tsitsipas beat Federer to reach his first Grand Slam semifinal in Australia in 2017 only to be hammered by Nadal, and he was overhauled by Djokovic at Roland-Garros this year. Medvedev was stopped by Nadal in the 2019 US Open final and by Djokovic in Australia in February.
This time, the road to the Grand Slam final is a bit less complicated.
Zverev, who won at the Olympics and the recent Western & Southern Tournament in Cincinnati, knows he and the others are close.
"We all miss them, we all love them to play forever," Zverev said of the big three. "(But) at some point they will have to retire.
"I think the Cincinnati tournament and other tournaments this year also showed that the competition and the rivalry that we have with the younger guys -- the top four or top five guys with Medvedev, Tsitsipas, myself, Rublev and (Matteo) Berrettini, we're having great battles, we're having very entertaining matches."
Medvedev, Zverev, Tsitsipas and Berrettini (at this year's Wimbledon), have all made Grand Slam finals. Medvedev, Zverev and Tsitsipas have all won the ATP Finals. Their time may finally be here.
"I've been two points away (from the title) last year here," Zverev said. "I'm very happy to be back here, because now I can feel like I can go out on that court and I can prove myself, whether I got better since last year, what actually happened. I feel like I'm playing great tennis this year.
"The top three guys, they've been dominating for the past 15 or 20 years. We might never see that again. Don't expect this group of guys to be the next Djokovic, Federer and Nadal. I don't think the four of us are going to win 20 Grand Slams in the next 15 years each. That's not how it's going to go."
Zverev is confident about the future but knows the high bar the big three established.
"I think we're going to split them among us maybe. But the dominance those guys had is something you see once in a lifetime probably. All of us, we're in that kind of path. We share kind of the same goals and aspirations.
"I personally believe that all of us have a good game to get to Grand Slam titles. It is important that we're able to showcase that level of tennis in these kind of tournaments as best as possible to represent our generation of tennis in the best possible way."
Djokovic remains the standard, but the pack is closing in.