Since taking over as Roar coach early last season, Mulvey has converted Brattan from a bit-part player to one of the key elements of the team who, when fit, is a certain starter in every game.
The English-born player was part of the squads that won consecutive A-League titles in 2010-11 and 2011-12, though with Erik Paartalu a fixture in midfield, he was not a regular first-team starter in either campaign.
Brattan did not take the field in the first of Brisbane's grand final victories, and came on as a late sub in the second.
This time around, however, the Roar's chances of success will depend in no small part on the 24-year-old's ability to dictate play from his deep-lying position in the centre of the pitch.
It is a role he has handled with aplomb all season. He has made more passes than any other Roar player aside from Thomas Broich, and has chipped in with three goals and three assists so far.
And Brattan said his elevated status in the side gives him a greater sense of achievement than in previous years.
"It's very satisfying," he said.
"I feel like, even though I've won two championships, I feel like I haven't personally won anything.
"Just playing regularly this season and being a big part of what we do, it's an absolute privilege.
"And I thank Mike for that, for giving me my chance and hopefully I can repay him with a win on the weekend."
Rather than feeling any extra pressure in grand final week, Brattan said he is relishing the build up.
"I don't really get nervous, to be honest, I just get excited," he said.
"It's a massive week, but personally I don't really want to treat it any differently.
"I'll keep it as normal as I can, and as relaxed as possible, and enjoy it.
"I just hope we win. If we can score a couple of goals, if I can get one, or get an assist or anything like that it would be great, it would be a bonus, but I'm just looking to do my job for the team and get the win."