When it's all said and done, Andre Agassi believes tennis superstar Roger Federer must be ranked alongside the likes of Jack Nicklaus and Michael Jordan as one of the greatest athletes of all time.
As with every rare Federer defeat, the doubters have been quick to relegate the Swiss master to yesterday's hero following his five-set Australian Open semi-final loss to Andy Murray.
But just as Murray and world No.1 Novak Djokovic were preparing to meet in a second straight grand slam final, Federer was plotting another successful season, unfazed by those declaring a changing of the guard in men's tennis.
"Nothing has changed," the 17-times grand slam champion and world No.2 said before leaving Australia.
"I've played these guys, what, 60 times? The three guys around me in the rankings.
"So we know each other really well. We play each other very close very often. Keep on trading wins and losses.
"Novak has done probably the best job getting more wins than losses. That's why he's ranked where he is.
"I enjoy the matches with Rafa (Nadal), Novak, and also Andy again (on Friday night). It's nice playing five sets against him. It was tough tennis. I enjoy that.
"So I go from here with a good feeling for the year. I didn't play a tournament leading in, so now obviously I know where my level is at.
"Also knowing I have even more time to work on my game, work on my fitness this year, it's something I'm excited about."
But regardless what the future holds for Federer, Agassi says the 31-year-old's legacy as a sporting immortal is secure.
Himself a four-times Australian Open champion like Federer, Agassi said the brilliant Swiss belongs in the conversation with Nicklaus, Jordan and company as one of sport's greatest ever.
"I'm biased in a sense that I think that tennis is one of the most comprehensive sports when it comes to endurance, when it comes to athleticism, when it comes to speed, when it comes to eye-hand," Agassi told AAP.
"It engages every part of what an athlete needs to be and I think the standard of athlete in tennis is finally now starting to make that recognised by people in other sports.
"So I am biased with what I think tennis brings to the table and I think what Roger's done in tennis is as commendable as what we've seen with Nicklaus in golf, or what we've seen with Jordan in basketball.
"The guy has single-handedly separated himself from a world-class field year after year after year in a way that's probably never been done."
Agassi, the sport's oldest-ever world No.1, says he has long given up being surprised about anything Federer achieves and believes even at almost 32 he is at the top of his game.
"I was ranked No.1 possibly even at 33," Agassi said.
"When I was ranked No 1 at that age, I felt better than when I was 25. I felt like I was a better player.
"Given that, I would assume that Roger probably feels like a better player because he's smarter.
"He's dealing with tougher competition. He might not win like he used to. But he himself (now) would beat himself (from back then).
"That would be a fair assumption."