Stefanos Tsitsipas celebrates his victory at the ATP World Tour Finals on Sunday in London, England. Photo: VCG

Stefanos Tsitsipas said he was ready for a breakthrough Grand Slam victory after winning the ATP Finals in London - but a glance at recent history invites caution.

The 21-year-old Greek was in bullish mood after he beat Dominic Thiem, having ousted Roger Federer in the semifinals, to become the season-ending event's youngest winner since 2001.

"I believe I'm really close to being crowned a Grand Slam champion," he said, after his 6-7 (6/8), 6-2, 7-6 (7/4) triumph in London on Sunday. "I know these are strong words that I say but I do feel I belong there."

But although Tsitsipas' victory feels significant, he is the fourth first-time champion in as many years at the season finale, which has proved a poor predictor of future success.

Last year, young German Alexander Zverev pummelled Novak Djokovic in the final but he had a miserable time at this season's Slams - while the Serb, 32, picked up the Australian Open and Wimbledon titles to take his overall tally to 16. Rafael Nadal, 33, won a barely credible 12th French Open title and added the US Open, underlining the fact that the old guard were still very much in charge.

No member of the "Big Three" - also featuring Federer - has won the season-ending ATP Finals since 2015, when Djokovic picked up his fifth title.

Djokovic was also the last ATP Finals champion to go on to win a major title. 

Injury-plagued Andy Murray has won only two trophies since he secured his sole ATP Finals title in 2016, crowning his strongest season.

And the lavishly ­gifted but inconsistent Grigor Dimitrov has not won a tournament since his 2017 success at the season finale.

The fact remains that despite all the razzmatazz surrounding the ATP Finals, it is the Grand Slams that are the true yardstick in tennis. 

Since 38-year-old Federer won his first Grand Slam title in 2003, the Big Three have collected an astonishing 55 out of the 66 majors on offer, with Murray and Stan Wawrinka also winning three apiece.

There has long been speculation over who would have the guts and talent to overthrow the established order.

Players such as Milos Raonic, Dimitrov and Kei Nishikori - members of a previous supposed "next generation," consistently failed to challenge the dominant trio. 

However, that is not to say that there's no hope for the younger players, who now appear to be getting closer.