It was one part of long apprenticeships that would help shape them into two of the best, most forward-thinking coaches in the AFL.
When the Swans take on Fremantle in Saturday night's preliminary final, one of them will again coach his side into a Grand Final.
Lyon began his coaching journey at the age of 30, when he became an assistant to Robert Walls at Richmond in 1996.
He had a terrific grounding in the coaching caper, spending four years at Tigerland, another four with Carlton and finally three with the Swans before being appointed head coach of St Kilda in 2007.
Following five years at the Saints, and three unsuccessful Grand Final appearances (including the 2010 draw), Lyon controversially moved to Fremantle ahead of the 2012 season.
Longmire's path to senior coaching was played out over a similar timeframe, but it all came at the Swans, where he was appointed as forward-line coach back in 2002.
He would fill a variety of assistant coaching roles before being appointed a coaching coordinator in late 2007, increasing his match day responsibilities with the eventual goal of replacing Paul Roos.
The two men had a 'Sliding Doors' moment in late 2006, when they were among a long list of candidates to replace the sacked Grant Thomas at the Saints.
Longmire was widely considered the favourite, but it was Lyon who came away with the job, leaving the former to continue his pathway at the Swans.
The two have close ties and clearly share a mutual respect.
"He's obviously a very good coach," Longmire said of his counterpart.
"We spent a bit of time traveling together doing some opposition analysis and we had some interesting times on the road.
"I know him pretty well obviously working with him (at the Swans) for a number of years and he's doing a good job with Fremantle.
"They've got some real talent on their team and they've embraced the way he coaches and he really knows his football."
Longmire, 42, has been right at the forefront of football’s modern trends, leading the Swans to premiership success last season.
The 46-year-old Lyon is also carving out an outstanding resume, with his Dockers now hosting a prelim for the first time in their history.
Both men also like to deflect attention away from themselves, insisting Saturday night is all about the players, not the men manning the phones.
"I know he's a really good person, has got great integrity … (and) I'm really au fait with their style," Lyon said.
"But it's not about the coaches. We're just part of the team.
"We help navigate and guide, but once the ball is bounced, it's all about the players really."
Longmire shares a similar sentiment.
"I guess if you go up against someone you know quite well it's an interesting experience, but at the end of the day it's not about he and I," he said.
"It's about the boys on the ground and hopefully the boys on the ground can get it done for us."
Even though it is seven years since he left the Swans, some of the players still remember the influence Lyon had on them.
One of those is Jarrad McVeigh, who was identified by Lyon this week as a central figure his Fremantle side will need to shut down at Patersons Stadium.
"He was hard on me, which was good for me," McVeigh said of Lyon.
"I learned a lot from him about the game and really rate him as a coach.
"Hopefully he doesn't coach too well against us this week, but I've got a lot of respect for 'Rossy' and the way he goes about it.
"He just wanted me to be the best player I could be and didn't want me to take short cuts.
"He's very smart tactically and he basically introduced the press to the game through St Kilda and now Freo have taken that to another level again.
"We look forward to tackling Rossy again this week."
