The Demons led 27-13 at halftime of Saturday night's match at Brighton Homes Arena, but Brisbane kicked five goals to one after the main break to seal the 6.9 (45) to 5.6 (36) victory.
Brisbane's Sophie Conway was best afield with 27 disposals, six tackles, three clearances, two goals and 527m gained, while Alexandra Anderson (28 possessions) and Orla O'Dwyer (26 disposals) were also big as the Lions posted their sixth consecutive win.
The fourth-placed Lions (8-3, 161.7 per cent) are now equal on points with third-placed Melbourne (8-3, 221.6 per cent).
Second-placed Hawthorn (9-2, 118.3 per cent) have to play unbeaten North Melbourne in the final round next week.
If Hawthorn lose as expected, Brisbane or Melbourne could nab second spot, with the Demons' superior percentage putting them in the box seat despite their loss to Brisbane.
The Lions face lowly Collingwood in Melbourne next week, while Melbourne take on the 13th-placed Cats.
"It's pretty special," Conway told the Seven Network after Saturday night's win.
"We've been building all season. The games we have lost, I still feel like we've been really competitive.
"It's nice to come up against a rival like Melbourne ... and get the four points."
Melbourne forward Kate Hore kicked 1.2 from 26 disposals to take her career tally to 98 goals, meaning North Melbourne's Jasmine Garner (97 goals) now has the chance to become the first person to reach 100 AFLW goals.
Both teams brought a finals-like tackling intensity in the first quarter, and it was Brisbane who dominated territory with a 15-6 inside-50 count.
Dakota Davidson hit the post from just metres away, while O'Dwyer's missed snap meant Brisbane went into the first break with the scoreboard only reading 4-0.
The second quarter featured moments of individual brilliance as Melbourne finally found their groove.
Tayla Harris kicked Melbourne's first goal via a mark, and Demons defender Tahlia Gillard followed it up a short time later with a brilliant goal-saving run-down tackle.
Hore's 98th career goal edged the Demons eight points ahead, but Brisbane defender Shannon Campbell's brave decision to run off her opponent to intercept a ball led to the Lions' first major - to Taylor Smith.
Two late goals to Eden Zanker ensured the Demons had a handy 14-point lead at halftime, but Brisbane hit back hard with the first four goals of the third quarter.
Conway was the biggest spark with two great goals, including one when she sold the dummy to an opponent before producing a 30-metre banana.
Melbourne defender Maeve Chaplin kicked her maiden AFLW goal after the three-quarter time siren to reduce the margin to three points, but Ruby Svarc kicked the only goal of the final term to seal the deal for Brisbane.
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