Seven months ago, Agassi was one of many former players and pundits who believed Murray was a victim of his time and that in any other era he would have won "multiple Grand Slams".
Murray never allowed himself to think about what might have been. Instead, he picked himself up, won the Olympics and then the US Open to break his Grand Slam duck in grand style.
Four months on, the consensus seems to be that Murray should now kick on, that his confidence will lead to more major success, and Agassi is now a believer.
"The way he got across the line in New York will have a huge impact on him because he had to step up and take it,'' he said.
''He couldn't just wait and watch somebody implode. He had to step up in that fifth set and step up against the biggest player on the biggest stage and take it, and he did.
"If his evolution is anything like mine, that was the real light switch that went off for me. I realised that I can't hope for somebody to lose. I have to want this enough to go after it. I think once that clicks in for him, you'll see him playing to their standard throughout the year and for a few years to come.''
The American has long been an admirer of the Scot's ability to unsettle opponents and take them out of their comfort zone.
But it is the world No.3's increased willingness to take the attack to his opponents, even when under immense pressure, which Agassi feels could see him dominate in 2013.
''This is Murray's year to really break through,'' he said. "He's come to understand what he needs to do out there.
"He has so many defensive skills that he does run the risk of falling into the temptation of being passive on the court. I think that can get him past everybody but not the two greatest players to ever play – Roger Federer and Rafa Nadal, not to mention Novak Djokovic, who is now starting to be part of that equation.''
Murray says he will not know how he will feel in Melbourne until he steps onto court for his first match tomorrow against Dutchman Robin Haase.
He is more relaxed than ever going into a slam, but is confident he will not allow any complacency to creep in; just because he won the US Open does not mean he is guaranteed to play well here.
Agassi expects Murray to increase his Grand Slam tally sooner rather than later.
"I believe he has very specific goals and objectives," Agassi said.
"He believes he can put a lot of numbers on the board.''