It was Green's fourth first-class century since the start of last season from when he is currently the leading run-scorer in the tournament. And despite currently not being able to bowl - he holds a first-class average of 21.53 with the ball - the debate around whether the time is already right to elevate him to the Australia squad will only intensify.
Green batted throughout the third day at Park 25 in Adelaide, resisting a range of tactics thrown at him by the New South Wales attack that - while missing Test stars Mitchell Starc, Pat Cummins and Josh Hazlewood - still boasted considerable quality, including Australia's lead long-format spinner Nathan Lyon.
"He's got a great cricket brain," Agar said. "They threw everything at him out there: bouncer plan, bowling wide channel, attacking the stumps, Nathan Lyon bowling a lot of overs - the best spinner in the world - and he had a really solid plan for everyone he faced. Even talking to him in the middle, he's really calm and composed.
"Whenever he does get the opportunity at the next level, I think he'll certainly be ready for that when it's there. But I just hope we don't put too much pressure on him, just let him go about his business because he's a beautiful player and [I] think he'll be [an] absolute superstar.
"To go in there and be 185 not out for a very young player, just shows he has maturity beyond his years and so much skill. The best part about it is he's a great kid - a great young guy. He learns, listens, works extremely hard on his game and assesses situations really nicely. And he looks really calm at the crease, nothing seems to faze him too much. For him to go out and get a really big hundred, again, is pretty special."
Australia head coach Justin Langer has previously cautioned against promoting Green too early - particularly while he recovers from the back problems that are restricting his bowling - but that is unlikely to temper the talk ahead of the proposed Test series against India in December despite Australia's XI being very stable.
"It would be hard not to hear bit of hype," Agar said, "but all I know is when he's out on the cricket field, he's just watching that ball as hard as he can. [He] loves batting, loves playing cricket and the scary part is that he's not bowling at the moment. He's a great bowler when he's up and running. To be able to play as a top four batsman and a frontline fast bowler is a great combination."
There is a hope that Green may be able to bowl in match conditions in this opening stage of the Sheffield Shield, which is being played entirely in an Adelaide hub. He already has two five-wicket hauls in first-class cricket, including a best of 6 for 30, but hasn't bowled since last November when scans revealed the early signs of stress fractures. His preparation for this season then involved tweaks to his action, which has taken time to settle.
"It's been awesome for his batting because he's just had time to nail that down and for us cement the batting spot for the team," Agar said. "[He has] amazing maturity, but for young fast bowlers you have to give their bodies time - they'll have some hiccups now and again, he's really tall and bowls quite fast. Whenever his body is right, he'll be able to manage both pretty well, I think."
Lyon, who had bowled the equivalent of 15 overs to Green during the innings, added to the praise and despite being on the receiving end of a day in the field, said it was good to see a young batsman with the ability to produce such a long innings.
"He was very, very impressive," he said. "Last time I saw him we had the big three quicks [Starc, Hazlewood and Cummins] bowling at him. So [today is] a different story, but obviously very impressive. [He's] very clear in his plans, played spin very well.
"[He has] a big future. It was really good to see, actually. He's 21 and not flustered by anything. Under pressure, he looked calm and clear in his plans. You've got to give credit where it's due and he definitely deserves that."