The Demons have been thrust into a cut-throat wildcard clash with Carlton at the MCG on Saturday night, having thrown away the chance at a top-six finish.
And while the Blues are the competition's hottest team, Petty is confident the Dees can keep confounding the critics.
They've done it all year, defying external expectations to reach the finals in King's first season at the helm.
"I look back at pre-season and the way we were playing, I thought that if we got 'Demon football' up and running then anything could happen," Petty told AAP.
"It took me a couple of games to get the feeling, but you've just got to have the belief.
"(The game style) is obviously different to what we were used to (under previous coach Simon Goodwin) - open the ground up and try to play a more free-flowing game.
"As a forward this year it's been very good. There's a lot more space to get into and I've been able to get on the end of a couple, which has been nice."
Petty has kicked a career-best 25 goals this season, all of those in his past 11 appearances.
The versatile tall could be the No.1 target for Carlton's premier defender Jacob Weitering in wildcard round, with teammate Jacob van Rooyen unavailable through suspension.
"I'm feeling pretty good at the moment," Petty said.
"I've been pretty happy with my form the last couple of months, that's for sure.
"I feel like I've built into the player that I've wanted to be. There's still plenty ahead, that's for sure."
Van Rooyen leads Melbourne's goal-kicking this year with 42 majors, ahead of Bayley Fritsch (35), Kysaiah Pickett (28), Harry Sharp and Petty (both 25).
Tom McDonald played forward in last week's loss to the Western Bulldogs and kicked two goals, while experienced teammate Jake Melksham returns against Carlton to add further firepower.
"We're functioning pretty well up forward," Petty said.
"It does hurt not having Jacob there, but we've got a few players that can come in and fill his role.
"We've still got belief in the players coming in from underneath to perform."
Pickett looms as the Demons' most likely game-breaker, having starred alongside fellow All-Australian Max Gawn and former St Kilda captain Jack Steele in an effective midfield unit this season.
"He's one of a kind. I don't think there's too many like him, though he reminds me a bit of Cyril (Rioli) back in the day," Petty said of Pickett.
"I wouldn't want to stand him anyway. I did it enough in pre-season as a defender and that's hard enough, let alone on game day when he's at another level.
"Hopefully he can be in some good form on Saturday night. He's shown he can all year, and to do it in front of 90,000 people, I think he's going to enjoy it."
Jack Viney and Xavier Taylor also return for the Dees, with defensive pillar Jake Lever (toe) and Matt Jefferson (knee) unavailable.
It is veteran midfielder Viney's first AFL game of the season, after just one VFL appearance on his return from Achilles and back injuries.
"He's been up and about for the last six or seven weeks since he got the green light to give everything a crack," Petty said.
"He's been good this year, sitting in the coaches' box every game ... he's been really handy for us."
Nick Haynes returns from an ankle injury to bolster Carlton's backline, but forward Will Hayward was unable to prove his fitness and could not be considered.
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