Stefanos Tsitsipas and Dominic Thiem will vie for one of the most prestigious titles in tennis at the ATP Finals on Sunday, with the suggestion the sport’s established order could finally be under threat.

For only the third time in 16 years the final of the season-ending tournament in London will not feature at least one of the ‘big three’. In fact, this is the second time in the last three editions of the event.

While Rafael Nadal, Novak Djokovic and Roger Federer continue to be the dominant forces on the Grand Slam stage, those fighting to bridge the gap are making important strides.

Federer: Next Gen have proved their point

Federer, whose hopes of a record-extending seventh title at the ATP Finals were ended by Greek Tsitsipas in the semi-finals, admitted the next generation of talent are catching up with the old guard with more consistent displays.

Thiem, far from a young player at 26, has already beaten Federer and Djokovic this week in the round-robin stage to reach the showpiece to add further credence to the belief the gap may finally be closing ahead of next season.

The last two standing.This year's #NittoATPFinals champion will be _______👇 pic.twitter.com/dAHQkVErWk

— ATP Tour (@atptour) November 16, 2019

“Does it feel like it might be the best year yet? Possibly,” said Federer after his defeat against Tsitsipas.

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Alexander Zverev believes that tennis will see a new Grand Slam champion next year, highlighting a few of the youngsters.

Alexander Zverev believes that tennis will see a new Grand Slam champion next year, highlighting a few of the youngsters.

“Then the only issue is that it seems like me, Novak, and Rafa are healthy, healthier than maybe in previous years, as well.

“So from that standpoint, I think they have proved their point this year by qualifying for the Finals, and also now Dominic showed again at these Finals, and winning five titles, beating all of us top guys.

Tsitsipas followed Thiem in beating Roger Federer at the ATP Finals this week Tsitsipas followed Thiem in beating Roger Federer at the ATP Finals this week Tsitsipas followed Thiem in beating Roger Federer at the ATP Finals this week

“Definitely it’s that next step they need, and seems like Dominic is in his absolute prime right now. Yeah, I would think so.

“But then I look at the list of who finished world number one, who has been world number one all these years, and it’s just crazy that it’s always one of us.

“But we are not getting any younger. So their chances increase not because we are getting worse but because they are getting better, I believe.”

ATP Finals at the O2

We delve into the archives and take a look back at previous ATP Finals played at The O2 Arena in London.

Tsitsipas breakthrough signals a changing of guard

Whether Tsitsipas wins the final or not on Sunday there can be no denying this has been a hugely impressive performance by the 21-year-old on his debut appearance.

He pushed year-end world No 1 Nadal all the way in his final round-robin match, having already secured qualification for the semi-finals, and then underlined his confidence and composure with a fearless performance against Federer.

Tsitsipas has compared the ATP Finals to a Grand Slam Tsitsipas has compared the ATP Finals to a Grand Slam Tsitsipas has compared the ATP Finals to a Grand Slam

It seemed only apt that it was the youngest player in the eight-man field to defeat the oldest and most successful player in the tournament.

Tsitsipas saved all but one of 12 break points he faced in the match, and triumph against Thiem – someone he has lost four times against in six meetings – would be the perfect tonic to end his season.

"A little bit more and I'll end up playing with all the players from the ATP World Tour Finals."This was @StefTsitsipas in 2016 as a hitting partner for @ThiemDomi.Tomorrow, the two will face off in this year's final 🤯📸: Stefanos Tsitsipas (IG) | #NittoATPFinals pic.twitter.com/kJCv3nyxQr

— ATP Tour (@atptour) November 16, 2019

“I’m proud of myself, how hard I fought, how concentrated I stayed in the break points,” said Tsitsipas, who was described “as hard as nails” by Federer.

“I didn’t crack under pressure. I was very composed and very mature in my decisions.”