Novak Djokovic could accumulate 25 grand slam titles by the end of his career, a figure that would have seemed inconceivable even a decade ago.
Twenty had always seemed like an impossible mark, while a quarter century wasn't even discussed, not even jokingly.
It might be now.
Remember Roy Emerson's record of 12 majors stood for 30 years before Pete Sampras passed it in 2000, and the American's mark of 14 was the sport's new Everest, but Roger Federer overhauled it within seven years.
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When Federer reached 20 in Melbourne two years ago that might have been seen as the ceiling - but not anymore.
The way the Serbian outlasted Dominic Thiem to win the Australian Open on Sunday night, despite not being in vintage form and overcoming a mid-match meltdown, was vintage Djokovic.
It was about grit and guts as much as superb skill-execution under pressure, and it's no longer a matter of if Djokovic can haul in Federer's mark of 20 majors, but when, because the list of players who can effectively compete with Djokovic remains very small.
Federer can, especially on grass (he was the better player for most of the epic 2019 Wimbledon final) but has only won two of their last nine encounters and hasn't bested him in a best of five sets scenario since 2012.
Nadal can, particularly on clay, but has also seen their rivalry tip the way of the younger man, and Nadal hasn't beaten Djokovic on a hardcourt since the 2013 US Open final.
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Gunslingers like Juan Martin Del Potro can, on their day, while the next generation, led by Thiem, will improve every year.
But will it be enough?
Djokovic should start favourite at both Wimbledon and the US Open, and if injuries don't intervene could have 19 slams by the end of the year.
He remains remarkably fit, lithe and strong, and his longevity will only be extended by plans to cut back his schedule and focus even more exclusively on the slams.
Djokovic turns 33 in May, and picking up eight grand slam titles after that milestone would be an out of this world achievement.
Federer, who has been the poster boy for revising what is possible in your 30s, has reached six major finals (three wins) since his 33rd birthday.
But Djokovic's game appeals as more robust, and he might not have the rivals that the Swiss has had to deal with, especially as Nadal becomes less of a factor away from clay.
Whatever happens, it's almost certain that Djokovic will surpass both Federer and Nadal (19) in a few years.
But it's also assured that he will never win hearts and minds like that duo, or Andre Agassi or Sampras, or other leading figures of the game have.
For whatever reason, Djokovic's achievements don't generate the same adulation.
He is admired for his great feats on court, but not loved and revered away from tennis like Federer and Nadal.
Maybe it is because he has so often been the spoiler, maybe perceptions of him have been sullied by various incidents over the years or maybe it is just that he doesn't seem particularly authentic at times.
But regardless, he's a tennis maestro, who will smash all kinds of records, and might even reach the 'impossible' quarter century.