There are four young players, Daniil Medvedev, 23, Stefanos Tsitsipas, 21, Alexander Zverev, 22, and Karen Khachanov, 23, all in the Top 10 in the ATP rankings. Two others—Matteo Berrettini, 23, and Borna Coric, 22—are in the Top 15 in the rankings.
Federer says they are now starting to push towards the top of the men's game.
"I am seeing big improvements now. Not like there were none beforehand, but now they are playing with the big boys and really able to challenge us, beat us, having good rivalries also within each other, which I think is important for them to improve as players," he told press in Shanghai.
"So I think it really creates good intentions to actually wanting to improve faster, and I see that right now.
"Each one of them has really shown some really good matches and some great runs."
And there is an even younger group behind them that is also climbing the ranks, notes Djokovic. It includes players like Felix Auger-Aliassime, Alex de Minaur, Andrey Rublev, Hubert Hurkacz and Denis Shapovalov, all ranked inside the Top 40.
"There is quite a similar, let's say right now, level of play, quality of tennis [with] these guys, but there are some guys that just are probably a bit separated from the group," said Djokovic. "Tsitsipas, still a NextGen, but he's kind of already an established Top 10 player and maybe not considered anymore as part of that group.
"But there is Felix and Denis and [Hubert] and guys like this that are playing really well, and on a given day they can really beat anybody."
They are also starting to play at that level more regularly, according to the Serbian. "I'm very pleasantly surprised by the level of consistency of especially Felix and Denis, you know, playing throughout the entire year, staying healthy and playing well, and being professional, committed. That's what you want to see," added Djokovic.
But particularly striking for the world No. 1 is the breakthrough of Medvedev, who's reached five successive finals, including a five-set loss against Rafael Nadal at the US Open, and won two events. The Russian also won from a set and a break down against the 16-time major champion in the semifinals of Cincinnati, recalled Djokovic.
"When you're full of confidence, obviously you go for the shots more. But he definitely possesses the quality in his game from back of the court. He's improved his movement, his fitness. He's got the big serve. He's got the height, and he uses angles very well. Backhand, hard to break that backhand. I mean, it's very flat," he said.
The emergence of this group has been intriguing to follow, including for the established champions still ranked above them.
"I think really it's a lot of guys, which helps for them to really make a move now," said Federer. "Yeah, they've got our attention, no doubt about that."
Top-ranked Djokovic and No. 3 Federer are the highest seeded players at the Shanghai Rolex Masters, and Medvedev right behind as the third seed.