The Roos' 29-point win over Carlton on Friday night leaves them knocking on the door of the top eight, but it hasn't left them assuming a rise into the top half of the table will easily occur.
"We haven't spoken about finishing top eight," McMahon told afl.com.au after the game.
"We just want to play a good brand of footy, which we did tonight and want to keep that going throughout the year.
"The belief is getting there. We haven't beaten a side above us or in the top eight [before Friday night] and Carlton is fifth.
"It's good to perform against a really good team but we've got to back it up against Port Adelaide next week."
The Roos' past two wins over the Blues and the Brisbane Lions have come after dazzling first terms where they've kicked 4.5 and 7.5 respectively.
McMahon said they had talked about fast starts after lethargic ones hurt them against the Western Bulldogs and Fremantle in the two previous weeks.
"We always want to get out to a flyer. It has been a bit of a focus for us," he said.
"We just want to keep the consistent pressure up throughout the whole game, which we did in the first quarter and I thought we followed through for the rest of the game.
"It makes it a hell of a lot easier when you do get out to a good start. You've got that buffer already."
The side's defence - and Lindsay Thomas' seven goals - was an influential part of Friday night's win with McMahon (23 touches, four rebounds), Scott Thompson (29 disposals - 14 contested) and Michael Firrito (22 touches, nine inside 50s) among the best players.
But McMahon said the win was largely a team effort.
"We felt like we played pretty well. It makes a big difference when the forwards and midfielders are putting a lot of pressure on and making the kicks long and high where we can come over and help each other out," he said.
"It does make our lives easier if the midfielders are pressing in and putting pressure on but it was good fun down there tonight."
