AT A PIVOTAL moment of the 2012 Grand Final, Sydney coach John Longmire made a positional move that would turn the game in the Swans' favour.

But it wasn't a star like Adam Goodes, Daniel Hannebery or Ryan O'Keefe at the centre of the tactical change, but an unsung hero who Longmire says was "one of the most flexible and smart players I've ever coached".

Having been 28 points up midway through the third term against Hawthorn at the MCG, the Swans conceded six of the next seven goals to trail by as much as 12 points 10 minutes into the last quarter.

It was then that Longmire put veteran utility Lewis Roberts-Thomson behind the ball in an attempt to halt the Hawks' momentum.

Having chastised himself for not pulling the trigger earlier in the game, Longmire didn't miss the opportunity the second time around.

"Hawthorn ... had a real pattern that if they kicked three goals in a row, they'd often kick five, six or even seven goals in a row," Longmire recalls on Coach's Office with Simmo, a new AFL.com.au series where premiership coaches reflect on Grand Final wins with 2018 flag winner, Adam Simpson.

"We had a plan going into the game that if they got three goals, we'd put someone behind the ball and just hold up the play a bit, just for that moment to make sure they didn't get five or six. We didn't do it earlier in the game, and I regretted it. I remember being a bit disappointed in myself that I didn't do it and I thought 'If it happens again, I'm not going to fall for it'.

"When it happened again in the last quarter, we just put Lewis Roberts-Thomson behind the ball straight away. It wasn't that we were fearful of not winning the game ... we thought the best way to win was to stop Hawthorn's momentum. And we were able to do that."

Having stopped the Hawks' momentum, the Swans rallied to kick the final four goals of the game to record a memorable Grand Final win in what was Longmire's second season at the helm.

Roberts-Thompson, who had been among Sydney's best in the 2005 and 2006 Grand Finals, again stood up under pressure, finishing the day with 14 disposals, seven marks, three score involvements and a goal.

"LRT was one of the most flexible and smart players I've ever coached and he played the role perfectly," Longmire says.

"For the whole last quarter, certainly for the last 15-20 minutes, I was on the phone to our runners ... about positioning LRT.

"Once we stopped their momentum and stopped them scoring, we pushed him up to be around the ball, he went third man up a couple of times and we were able to get the momentum back."

Watch John Longmire's full episode of Coach's Office with Simmo in the video above