By Martyn Herman

LONDON, Nov 17 (Reuters) – Rafael Nadal will end the year as the world’s top-ranked player and the “big three” retained their stranglehold on the Grand Slam titles, but when Stefanos Tsitsipas was crowned ATP Finals champion on Sunday it felt like a watershed moment.

“I believe I’m really close on being crowned a Grand Slam champion. I know these are strong words that I say, but I do feel like I belong to be there,” the 21-year-old Greek boldly claimed after beating Dominic Thiem.

There have been false dawns before of course. Germany’s Alexander Zverev, like Greek Tsitsipas, was also 21 last year when he beat Novak Djokovic to win the season-ender in London.

Zverev could not back it up in this year’s Slams, two of which were won by the 33-year-old Nadal and two by the 32-year-old Djokovic. They have 19 and 16 majors each while Roger Federer, at 38, will still believe he can add to the record 20 he has accumulated during his extraordinary career.

But for the first time, that golden trio will be having an anxious glance over their shoulders. The past week in London has revealed a new fearlessness in the generation of 20 somethings expected to fill the void when they call it a day.

Austrian Thiem, who at 26 is an established force, got the ball rolling when he beat Federer on the opening day of the ATP‘s exclusive year-ender.

The following day Germany’s Zverev beat Nadal for the first time in his career while earlier that day Tsitsipas marked his tournament debut by beating 23-year-old Russian Daniil Medvedev, who reached this year’s U.S. Open final, for the first time

It did not stop there. Thiem then beat Djokovic and Medvedev should have beaten Nadal, losing from 5-1 up in the decider.

On Saturday, Tsitsipas silenced the Federer fan club to eclipse the six-time champion in straight sets to reach the final — beating the Swiss maestro with the kind of attacking game Federer has trademarked.

MISSING TRIO

With Nadal and Djokovic bumped out in the group, Federer’s semi-final defeat meant it was only the third time since 2002 that at least one of that trio had not reached the final.

That may have disappointed some, but the quality and intensity of Sunday’s final in which Tsitsipas beat Thiem 6-7(6) 6-2 7-6(4) to become the youngest champion at the season-ending tournament since 2001, had the O2 Arena audience enthralled.

“The question to be asked is where is the road going after Djokovic, Federer and Nadal and after this week I think we are in safe hands,” former world number one Boris Becker said.

With the likes of Medvedev and fellow Russians Karen Khachanov and Andrey Rublev, Canadian duo Felix Auger-Aliassime and Denis Shapovalov, Australia Alex De Minaur and Italians Matteo Berrettini and Jannik Sinner, not to mention German Zverev, gathering en masse, change is brewing.

Thiem, beaten in successive French Open finals by Nadal, believes next year could herald a new Grand Slam champion.

“I think that for sure we can do it next year. We are all playing great tennis,” Thiem said. “Sascha (Zverev), Stefanos, me, some other guys. I’m pretty sure that we’re going to see a new and young Grand Slam champion next year.”

Tsitsipas wisely pointed out, however, that over best-of-five-set matches, beating the big three remains a massive challenge, even if he did down Federer in Australia.

“That’s a really difficult task to do for players,” he said. “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.”

On the evidence of the past seven days the waiting game may be about to come to an end. (Reporting by Martyn Herman; Editing by Ken Ferris)