With Lachie Neale and Zac Bailey leading the way on Friday, the Lions took their time to shrug off the visitors in an otherwise dominant second half to maintain their unbeaten home record with a 13.19 (97) to 12.9 (81) in front of 28,561.
Needing a win to keep the faint finals hopes flickering, the Swans took it to their more-fancied rivals from the outset with fierce pressure.
It took Brisbane until late in the last quarter to break far free and consolidate their place in the top four with their 41st win from their last 44 regular season matches at the Gabba.
With questions being asked of their premiership credentials after two defeats either side of their mid-season bye, the Lions' victory was crucial but won't convince the doubters.
The Lions should have killed off the match earlier but kicked 6-14 after halftime as they dominated the inside 50s but allowed Sydney to stay in the game, much to the frustration of coach Chris Fagan.
"No disrespect to Sydney but we should have won by a lot more," Fagan said. "It shouldn't have been a game we won by 16 points, it should have been a five or six-goal win.
"We were quite a dominant team ... we were completely in control but couldn't finish off.
"That was a little disappointing. Tonight we found a way to win but it should have been a bit easier."
The big positive for Brisbane was the performance of father-son draftee Jaspa Fletcher on debut who looked assured and produced some brilliant touches off the wing.
Rubbing salt into the wounds for last season's grand finalists Sydney, who have now dropped to 5-8 for the season, Sam Wicks was placed on report for high contact.
Wicks is in hot water for his second-quarter high shot on Ryan Lester when he leapt off the ground and collected the veteran defender with his forearm.
Missing injured stars Isaac Heeney and Lance Franklin, the Swans started strongly and ensured the game was played on their terms as they took an early two-goal lead into quarter-time.
James Rowbottom and Luke Parker were pivotal around the stoppages and denied Brisbane any clean possession until late in the first half.
Milestone man Cam Rayner kickstarted the Lions in a five-goals-to-two second quarter, punishing Ollie Florent for taking him on out of the goal square.
The highlight of the term was a scintillating counter-attacking goal by Fletcher who received the ball on the centre wing and side-stepped Aaron Francis before nailing the finish.
It gave Brisbane the lead for the first time since the opening and was a savage blow to Sydney who had control after setting up camp in their forward 50.
Lions dangermen Charlie Cameron was kept quiet, restricted to just seven touches and no goals, by Harry Cunningham who received lavish praise from his coach, John Longmire
"Harry was just outstanding," said Longmire. "Charlie Cameron is a superstar, and it's not an easy thing to do to play on a bloke like that."
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