Andre Agassi is urging tennis fans to soak up every opportunity to see Rafael Nadal and Roger Federer in full flight as a once-in-a-lifetime era threatens to draw to a close.
Nadal takes on American prodigy Frances Tiafoe in the Australian Open quarter- finals tomorrow as the Spaniard continues his pursuit of a second title in Melbourne, a decade after his unforgettable five-set final triumph over Federer.
But hopes of the two tennis titans rekindling one of sport's most enduring individual rivalries in the semi-finals have been scuppered by 37-year-old Federer's fourth-round loss to Greek sensation Stefanos Tsitsipas.
Federer was offering no guarantees he'd return to Melbourne in 2020, but rather signalled the potential end to his colossal career with the revelation he'd return to Roland Garros this year for the first time since 2015.
Agassi is refusing to predict when the end might come for Federer and Nadal but, with Nadal turning 33 in June, the former world No.1 knows the 17-times major winner's battered body can't play on forever.
"I'm sick of being wrong, quite frankly. These guys are redefining the bar and expectations," Agassi told AAP when asked to predict how much longer the two living legends have left in the tank.
"Watching how Roger goes through his matches, it's like he has another gear you never knew he had and he makes up for other areas that might not be like they once were.
"But he makes a lot of good decisions out there.
"Rafa needs his body a lot more than Roger does just based on how he plays and his urgency, the physicality.
"Roger has more options to put less kilometres on his body.
"So all I can say is that when it comes to an end, it happens fast.
"To say when that's going to happen, it's not possible."
Throw in Federer's 20 majors and Novak Djokovic's 14 and the superstar trio have amassed 51 grand slam singles titles between them, while sharing the top ranking for a staggering 740 weeks over the past 15 years.
"It's an incredible generation. It will be sad when it's gone," Agassi said during a promotional trip to Melbourne for Lavazza.
"But there's always that anticipation of change. Sometimes the disappointment, too, of change, where it kind of stays open for a little while.
"But you can't make those predictions and speculation. You just count your blessing today and see what happens."