But reflecting on the years since, the soon-to-be NSW lock says plenty has changed since his early years as Maguire's charge.
Few current players appear better suited to the Origin cauldron than Cronulla captain McInnes, who holds the record for most tackles in an NRL game (84) and has had so many dental mishaps on the field he wears false teeth off it.
Cronulla captain Cameron McInnes credits Maguire with helping instil his trademark toughness. (James Gourley/AAP PHOTOS)
McInnes said he was "over the moon" when Maguire called on Sunday evening to confirm he'd be making his Origin debut in the series opener next Wednesday.
"It was special coming from him because he gave me my debut (at Souths)," McInnes said.
Also on Origin debut, coach Maguire has selected a team with four forwards on the bench, signalling a rip-and-tear approach will be taken into Accor Stadium.
That will suit McInnes and fellow Blues squad members Angus Crichton and Luke Keary, who also earned their NRL debuts under Maguire at the Rabbitohs.
"We spoke the other night about how grateful we are for the training he put us through and the lessons he taught us," McInnes said.
"At the time, you only think about how hard it is, but we knew nothing else.
"So now we know how to deal with anything because of what we were dealing with back then."
Cameron McInnes, pictured at Blues training, says he has learnt a lot from Maguire over the years. (Dan Himbrechts/AAP PHOTOS)
McInnes owes more than just that to Maguire.
When Damien Cook began emerging as the Rabbitohs' first-choice hooker in 2016, Maguire signed off on McInnes's early release from the club, paving the way for his move to St George Illawarra.
It was at the Dragons that McInnes transformed into an elite NRL player and earned selection in the Blues' extended squad for the 2020 post-season series.
"I was lucky to get the opportunity to leave early and get a fresh start. I'm sure that was hard for 'Madge' (Maguire), but I'm really grateful," McInnes said.
He might have been tough from the early days, but McInnes says he has come a long way since his time as a fresh-faced Rabbitoh.
After recovering from a knee injury that kept him out of the entire 2021 season, the 30-year-old transformed into a fully fledged, mobile middle forward on joining the Sharks.
Off the park, he has matured as well.
"I was my own worst enemy sometimes at Souths," McInnes said.
"Some guys are ready for first grade physically, but mentally it takes them a bit longer, and I was probably one of those.
"I didn't realise what it took to be a first-grader, what you need to do for the team, what's important and how you play your game."
With that growth in mind, McInnes feels his full-circle moment under Maguire has come at a good time, but that there's more to be written in his story.
"I feel like I'm playing better than I (ever) have," McInnes said.
"That's also why, touch wood, I think there's a few more levels to get to. I've only been playing this position (lock) for a couple of years, I still want to get better before I hang up the boots."
14°C