The Demons dominated from the start on Saturday at Ikon Park and mauled the last-placed Magpies 11.8 (74) to 4.3 (27).
Melbourne will now sweat on the result of Saturday night's match at the same venue between Carlton and Essendon.
The Bombers are half a game behind the Demons after Essendon's Dreamtime in Darwin draw a week ago with Richmond.
No other side in the top eight will want to play a final against Melbourne, who have won five of their past six games to storm into top-eight contention.
AFLW great Stacey Livingstone was chaired from the field after her last game. The Collingwood defender had a shot at goal in the final quarter of her 77th match, but kicked it like a back and only managed a behind.
Collingwood defender Stacey Livingstone has retired after a distinguished AFLW career. (Con Chronis/AAP PHOTOS)
At the other end, Melbourne captain Kate Hore kicked three goals as she returned from the quad problem that made her a late withdrawal last week.
The Demons could well rue Hore's absence a week ago, given they lost to Hawthorn by only six points.
"Fingers crossed - now we wait," Hore told Fox Footy after the match.
"But I'm super proud of the girls' effort today, regardless of what happens tonight. We just wanted to come out here and finish our season strong - either bring that momentum into next week or next season.''
She said the team would watch the game together at a pub, "and hopefully stay sober for the whole night".
Eliza McNamara also starred for the Demons, racking up 21 possessions by half-time and finishing with 32 for the game.
Collingwood's Brittany Bonnici (centre) and Eliza McNamara of the Demons contest the ball. (Con Chronis/AAP PHOTOS)
Melbourne veteran Rhi Watt revealed in a mid-game interview that she will also retire whenever their season ends.
Collingwood showed some promise for the future, with young defender Lucy Cronin impressing again.
When Brittany Bonnici kicked a goal either side of quarter-time, the Magpies only trailed by seven points.
But that only sparked the Demons into action and they kicked the last four goals of the half to kill off the game, going on to kick their highest score of the season.
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