World No.1 Novak Djokovic has pointed to the spate of recent titles won by tennis' next generation of stars as evidence that a change is coming at the top of the men's game.
Germany's Alexander Zverev is the latest of the NextGen stars to taste success after claiming the Madrid Open title over the weekend, with victory against Italian Matteo Berrettini in the final.
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In doing so, he became just the fourth player after Djokovic, Roger Federer and Rafael Nadal, to win the event more than once.
Zverev returns this week to Rome, the site of his first Masters title in 2017, fresh off a second triumph in the Spanish capital - and fourth overall at this level.
However, the year's other Masters champions - Stefanos Tsitsipas and Hubert Hurkacz - were both first-time winners of the prestigious titles.
At 22, Tsitsipas is the youngest out of that group, with Zverev and Hurkacz both 24.
Throw in players such as grand slam champion Dominic Thiem (27), World No.2 Daniil Medvedev (25) and World No.7 Andrey Rublev into the mix, and it's an exciting group of stars challenging the 'Big Three' in men's tennis - Djokovic, Nadal and Federer.
Speaking ahead of his Italian Open defence, Djokovic himself admitted that the Big Three's stranglehold on the men's game is under serious threat.
"The results are showing that," Djokovic said, after sitting out the Madrid Open.
"There are guys like Tsitsipas, Zverev, Berrettini, (Andrey) Rublev that are winning against all of us and playing a lot and building their ranking points. (Daniil) Medvedev as well, of course, and challenging for the top spots.
"Dominic Thiem of course has been there for many years. It's inevitable that it's going to happen. The change on the men's rankings, top of the rankings is coming.
"Whether it's going to happen in a month or a year or whatever, I don't know."
Djokovic in March eclipsed Federer's record for the most weeks spent at number one. This week marks his 320th at the top of the men's game.
Djokovic has all-time record in sights
But the Serb, who won his 18th major at the Australian Open in February, insisted his focus now is on surpassing Federer's haul of 20 Grand Slams - a record the Swiss ace shares with Nadal.
"I'm not personally paying too much attention anymore to the rankings as much as I am to my game for the Grand Slams. Those are the biggest focus tournaments right now at this stage of my career.
"I have managed to achieve the milestone of the historic ranking No. 1, and that was the focus up to recently. Now it's more about really trying to peak at Grand Slams and make those count for my career."
Djokovic has played just two events since winning a record-extending ninth Australian Open title in 2021. He lost to Dan Evans in the last 16 at Monte Carlo and was beaten by Aslan Karatsev in the semi-finals at home in Belgrade.
He is gearing up for another bid for a second Roland Garros title, as he attempts to become the first man to win all four Grand Slams twice since Rod Laver in 1969.
Djokovic lost to Nadal in straight sets in last year's French Open final.
"I didn't have too many matches. I didn't play so great in Monaco and Belgrade, but I'm hopefully going to change that here in Rome and then another week in Belgrade before the French Open," he said.
"Four tournaments before the French is I think enough in terms of match play.
"So I'm building my fitness and I'm building just my game slowly step by step in order to peak in Paris. That's definitely where I want to play my best."
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