West Coast's bid to land a top-two berth faces a nervy Gabba test after they suffered a 17-point loss to Melbourne at Optus Stadium on Sunday.
Eagles forward Jack Darling lasted just 10 minutes before being forced out of the game with concussion, and the Demons capitalised to post the 16.12 (108) to 14.7 (91) win in warm conditions.
Melbourne's 13th win of the season secured their spot in the AFL finals, ending the club's 12-year drought.
West Coast would have locked up a top-two berth with victory, but they now need to beat Brisbane at the Gabba next Sunday in order to secure two home finals.
If they lose to Brisbane, they could drop as low as fourth.
Eagles coach Adam Simpson said it's important for his side to put the disappointment of the loss to Melbourne behind them.
"Look if you had have said at the start of the year that for the last round you're playing an away game for second spot on the ladder, we would have taken it," Simpson said.
"That's what's up for grabs. We can't miss top four now. Every club's internal goal is to get to top four if they can, and now we've got an opportunity to finish top two.
"We're not taking anything lightly. We'll be playing our best available, and we'll throw the absolute kitchen sink at this game."
West Coast led Melbourne by a point when Mark LeCras kicked truly at the 19-minute mark of the final term.
But the Demons booted the last three goals of the match to snare the win.
Jake Melksham booted four goals, while Tom McDonald and Mitch Hannan kicked three goals each.
Willie Rioli booted three goals for the Eagles, but West Coast lacked a good target in attack once Darling went down.
Darling was concussed by a strong Oscar McDonald tackle.
Although the tackle wasn't malicious, the incident could be looked at given one of Darling's arms was pinned as McDonald fell down on top of him.
Demons midfielder Aaron Vandenberg could also be in strife for a glancing elbow to the head of Eagles goalsneak Willie Rioli in the first quarter.
Melbourne entered the match with the unenviable record of being 0-7 against the competition's top-nine sides this season.
Demons coach Simon Goodwin was proud of his team's ability to put aside the external criticism and secure a finals berth, ending 12 years of "misery" for the club.
"I think it's just a step for our footy club," Goodwin said of securing a top-eight berth.
"It's emotional because as a coach and a playing group you feel that expectation. You feel that added pressure because we have had 12 years without playing finals."