ATP Finals: Greek ace Stefanos Tsitsipas stuns Roger Federer to reach London final (VIDEO)

In a tournament that has seen the biggest names in tennis usurped by the younger generation, the one remaining superstar in the final four, Roger Federer, was dumped out of the tournament by Greek star Stefanos Tsitsipas.

Tsitsipas ran out a relatively comfortable victor at The O2 Arena in London as he defeated the six-time ATP Finals champion in straight sets, 6-3, 6-4.

The 21-year-old already made history for his nation by becoming the first player from Greece to reach the ATP Finals in 50 years. But now, after a superb week in London, he finds himself in the final itself after ousting Swiss legend Federer in the semis.

Federer missed a host of chances to break Tsitsipas, as he blew his first 10 break points of the match, while his own serve was under constant threat after Tsitsipas broke him in his first service game of the match.

With Federer missing chances and wasting opportunities, Tsitsipas played strong, determined tennis as he took full advantage. And when he closed out the ninth game after a 13-minute battle, it felt like the Greek young gun may have broken Federer's usually steely resolve.

Clearly struggling, Federer lost his serve to love early in the second set to put Tsitsipas firmly in the driving seat, but offered his fans a glimmer of hope when he broke straight back in the next game for his first break of the match.

But Tsitsipas could see the finish line, and would not be denied as he went for his shots with gusto to eventually take the second set 6-4 and claim a huge scalp in the process.

Tsitsipas will face the winner of the second semi-final between defending ATP Finals champion Alexander Zverev and Austrian star Dominic Thiem in Sunday's final.