Having been drafted with the Saints' second pick last year, at No.18 overall, he started in St Kilda's depleted midfield, collected 21 disposals, and was one of his side's best players in the 17-point win.
It was a performance judged good enough for Dunstan, 19, to become the first Saint nominated for the award since Arryn Siposs in round 15, 2012.
But little more than a week earlier, Dunstan was left cursing his luck as his prospects of making his AFL debut looked in doubt.
A rolled ankle at training had flared up, and after a full first pre-season which had gone so well, he was suddenly wondering whether an injury would stop his surge towards a round-one start for the Saints.
"I trained right through to the end and it was fine, but about 15 minutes after I left training I sat down and it really stiffened up," Dunstan told AFL.com.au.
"That night I was probably a little bit nervous. We had the season launch and it was pretty sore during that and I was in a fair bit of pain. But it wasn't too bad the next morning and I went from there."
While the mood at the club was buoyant after the win, Dunstan wasn't sure whether his summons to meet with the coaches on Monday morning was a good or bad sign.
"I got a phone call from the footy manager Chris Pelchen and I didn't know if I was in trouble or what I'd done," Dunstan said. "I went in and 'Richo' (coach Alan Richardson) and all of the coaches were in a room and he told me I'd got the nomination.
"I honestly hadn't even thought about it so it was a nice surprise."
Since joining the Saints, Dunstan has impressed with his work ethic and ball-winning ability.
Against the Demons he had five clearances, and feels that part of his game has stepped up under some regular tutelage from champion St Kilda midfielder Lenny Hayes.
St Kilda has a 'buddy system' in place, with Hayes assigned to Dunstan, watching playing vision together, reviewing games and helping him transition into an AFL career.
"He's been massive for me so far. We've worked together closely for the last three months," Dunstan said.
"We go through vision together, we normally do all our extras before and after training together, and during the meetings we talk and have one-on-one chats. We've also been out for dinner a couple of times.
"He's an absolute ripper and I couldn't have asked for anything more."
Along with Dunstan, new Saints Jack Billings and Eli Templeton also featured in the club's win over Melbourne. Hours before the game Dunstan was chatting with Templeton about what it would be like, and how things might go.
Now that he's had a taste of things, he's keen for more.
"I've just got to try to cement my spot and hopefully I get another opportunity," he said.
"This time last year I was sitting there and they were talking about the guys from last year who had just played in round one. You sit there thinking 'How did they do it?'
"At some stages I sit back and take it in. I'm pretty lucky, I think."
Twitter: @AFL_CalTwomey http://afl.to/callumtwomey
