THROUGH it all, Paul Roos and Ross Lyon have remained in close contact. First as Fitzroy teammates, then as good friends with coaching aspirations and, for three years, as co-conspirators in their roles as senior coach and assistant coach at the Swans.

"We've probably been on the phone on a weekly basis for 20 years," said Lyon of a friendship that endured Roos's move from Fitzroy to Sydney.

But as they prepare to meet for the first time as rival senior coaches when the Swans play St Kilda at Telstra Dome on Saturday night, Lyon is not expecting much pre-game banter.

"We'll probably just go about our own business," he said. "We might see how the kids are going. If we do talk we'll have a bit of a chuckle about how everyone is building it up."

Lyon acknowledges that his new job has slightly altered the dynamics of the relationship. "You have to be a bit more cautious sometimes about the things you can and can't say," he said.

For his part, Roos said he would probably call Lyon later in the week. "I feel like our friendship overrides anything else," he said.

That doesn't extend to a few subjects that have been off-limits since Lyon joined St Kilda, however. "I don't want to sound like a Nick-know-it-all telling [him] how to do his job or making unwarranted observations, so I probably try not to ask too much about his team," he said. "I don't want him to think I'm prying or to feel he has to hide things." The big question on Saturday night is whether Lyon's inside knowledge of the Swans will give the Saints an advantage.

As the Swans' midfield coach, Lyon was given much credit - or, from the AFL, the blame - for Sydney's game plan, particularly their ability to create and win stoppages. Such an intimate understanding of the Swans' tactics and personnel would seem to provide a big edge.

But Lyon said he was the man who knew too much.

"It might be a disadvantage because they've changed a few things this year and sometimes you can have too much information," he said.

"Anyway, the whole world knows how Sydney play but not many teams beat them."

Lyon said the one piece of advice Roos gave him before he left Sydney was to "be true to yourself". Yet many experts believe he is attempting to replicate elements of the Swans' game plan at St Kilda, particularly by making them more accountable for opponents and competitive at stoppages.

Although he is drilling his team in the fundamentals, Lyon denies he is creating St Sydney. "People are getting carried away with that and I think it's been a little bit unfair," he said. "The statistics show we are playing differently. They have almost double the stoppages we do. We're playing a more up-tempo brand of footy. Our forwards are different, our midfield is different."

Accordingly, Roos believes the big advantage Lyon holds is not his knowledge of the Swans' game plan but that, as a new senior coach, no one has had time to work him out.

"Not that he knows what we are doing, [it's more the fact] that none of us know what he has put in place," Roos said.

One thing Lyon will not do is underestimate the Swans, a mistake he said was made too often in his time at the club.

"To me, everyone underrates the Swans and their star content," he said. "They've got eight or nine of the best players in the competition."

Lyon includes Barry Hall, Adam Goodes, Brett Kirk, Michael O'Loughlin and Ryan O'Keefe in this category. "That's a fact you can't dispute - they are an elite team," he said. "And with [Peter] Everitt and [Darren] Jolly, they've probably now got the best ruck combination in Australia."

It's the topic for a good conversation. But it's certainly not one Roos and Lyon will be having this week.