Eight-times Grand Slam champion Andre Agassi has been amazed by the soaring quality of men's tennis since he retired and believes he would struggle to compete in what he believes is a "golden age" of men's tennis.
On his first visit to Melbourne Park since calling time on his career, Agassi said Roger Federer, Rafa Nadal and Novak Djokovic were arguably the three greatest players of all time and Andy Murray had shown he was capable of competing with them.
"It's been amazing watching the standard continually sort of get better," the 42-year-old American told a news conference on Friday.
"You wonder how it's possible to continue at that sort of rate. What Federer did when he came and when I said good-bye, a lot had to do with what I knew was untouchable.
"It's just a different standard of tennis. It's different rules of engagement when guys can do what these guys can do.
"I don't recognise it from a standpoint of strategy, because I counted on getting somebody behind in a point and then slowly smothering them."
"But nobody's behind in a point. You never know when they're behind in a point. That would have eliminated any ability I had to move forward in the court.
"That means I would have had to be a different player, would've had to have a different body. It means the game has gotten a lot better."
With Nadal absent injured, Federer and Murray face off later on Friday to decide who meets Djokovic in Sunday's final.
Among them, the Big Four of men's tennis have won all bar one of the 28 Grand Slam titles over the last seven years.
Federer leads the way with 17 titles, Nadal has 11 and Djokovic five, while Murray broke into the winners' circle for the first time at last year's US Open.
It is the quality of the tennis they play that has most impressed Agassi, however.
"Fed raised it, Nadal matched and raised it, Djokovic, for that intense little period of time, raised it higher," the four-times Australian Open champion added.
"It seemed like last year settled down a bit, and now all of a sudden Murray is in the equation of where is he going to go."
"But when I see those top three guys, I see what history will say is the golden age of tennis. You're talking about arguably the three best guys.
"Djokovic will still need some distance to cover, but best of all time, if you're having that discussion in the same generation, it's remarkable."
With Murray now entering the equation, Agassi said he could only see standards getting better and better.
"Something tells me it's not going to stop here," he said. "History would prove that it's never going to stop. So every five years it seems to click up a different level.
"It's a remarkable era. You know, Murray is doing this now in a time that's incredible, and yet you wonder, can he really establish himself as one of those guys."
"The answer is, yeah, he can. He's coming into his own now. He believes now, and so now you're talking about four guys."
"If it was one person, I would say, okay, he came at a good time or he squeezed in a window. But they raised each other."
"I mean, Nadal was No,2 in the world for how long? How much did he have to win just to even see the taillights of Fed? Yet he beat him and he beat him and he beat him and he earned it."
"Then Djokovic comes by ... those guys have changed the rules out there."