Melbourne's loss to Collingwood on Saturday brings West Coast back into contention for a finals spot.
An Essendon loss to Fremantle looks unlikely, so West Coast's fate will hinge on their result against Adelaide in order to jump Melbourne on the ladder.
Their percentage is still below Melbourne, so a win over Adelaide won't be enough: they need to rely on a percentage boost.
We've done the maths: they need to win by at least 21 points to ensure their percentage climbs above Melbourne's.
A win of that size will see the 0.9% percentage gap between them and the Dees eradicated.
Strangely, the exact margin required may differ, depending on Adelaide's score.
West Coast can win by 20 points to leapfrog Melbourne, as long as they keep Adelaide's score to 70 or less.
A 90-70 win for the Eagles will see their percentage jump to 105.223% - that's 0.001% ahead of Melbourne - but a 91-71 win won't be enough, with their percentage then 105.221%.
If the game gets high scoring, they might need a 22-point win, too - a 111-90 win over Adelaide won't be enough.
So it may depend on Adelaide's score if the margin hovers around the 20-point mark.
Triple M's James Brayshaw summed up how precarious Melbourne's fate is.
"Melbourne, now, have to wait,” he said after the Collingwood/Melbourne game.
“The worst possible place to be after your final home and away game."
West Coast's required margin of victory to jump Melbourne:
19 points if they can keep Adelaide's score under 50
20 points if they can keep Adelaide's score between 51 and 70
21 points if they can keep Adelaide's score between 71 and 90
22 points if they can keep Adelaide's score between 91 and 110