'That hasn't happened ever': Roger Federer bemoans rare moment in loss

Stefanos Tsitsipas has silenced the raucous Roger Federer fan club as he knocked the 20-times grand slam champion out of the ATP Finals.

Tsitsipas is 17-years younger than the mercurial Swiss maestro, but showed calm under pressure to 11 breakpoints throughout the match.

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He even fought off a vociferous pro-Federer crowd to reach the final in his first-ever ATP Finals.

And the Greek hopes to one day be as popular as the Swiss great.

Roger Federer reacts in his semi-final singles match against Stefanos Tsitsipas in the ATP World Tour Finals at The O2 Arena on November 16, 2019 in London, England. (Photo by Justin Setterfield/Getty Images)

Only the most one-eyed Federer followers could not have been impressed with the Tsitsipas's 6-3, 6-4 victory, achieved with the kind of tennis they are used to seeing from their idol.

With his fearless, eye-pleasing groundstrokes, regular forays to the net and booming serves, the engaging 21-year-old certainly has much to applaud.

But he knows the Federer followers will be tough to win over.

"I hope they like me when I play out on the court, because I feel like I have a lot of things to offer for tennis," Tsitsipas said.

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"And I would love to see one day potentially a fan base and people come to the court like they do for Roger, because it's an army. And you need that. You need an army like this.

"I want to feel connected with people. I want to be known as a good tennis player because that's what the fans want to see. They want to see a good personality."

The way Tsitsipas responded when put under intense pressure on Saturday was impressive.

He saved 11 of the 12 break points he faced and survived an epic 13-minute game when he served for the first set at 5-3, sealing it at the seventh time of asking.

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For Federer, it was a case of what may have been after two botched overheads in the same game cost him a break and his inability to take advantage of his openings.

"I think getting broken with missing two smashes in one game, that hasn't happened in a long, long time or ever," the 38-year-old said.

One suspects Tsitsipas's style would get the nod of approval from Federer and the six-time ATP Finals champion was generous in his praise for the world No.6.

“I have to credit him for pushing me to not playing at the level I was hoping to today," Federer said.

"He did come up with the goods when he had to, and he was better than me today."

Tsitsipas will face Austrian Dominic Thiem in the final.

Thiem having knocked Alexandre Zverev out in the semi-final means there will be a new ATP Finals champion.

With AAP