In a game with 17 lead changes, Joe Daniher had the final say on Thursday when a Richmond spoil landed at his feet and he soccered through the go-ahead goal with 64 seconds to play at the Gabba.
The 16.10 (106) to 16.8 (104) win means Brisbane will now play the loser between Sydney and Melbourne, while it's curtains for Richmond, who had entered the finals in hot form.
"The nerves were jangling, especially when we got in front with about a minute to go," Chris Fagan said.
"Richmond didn't deserve to lose and neither did we.
"There's not many better games of football that I've been involved in."
Brisbane, who boasted a sorry 1-5 post-season record in the last three years, lost Oscar McInerney in the third minute to concussion while Dion Prestia (hamstring) was a costly loss for Richmond before halftime.
Tom Lynch (three goals), who had put Richmond 16 points clear in the third term before Brisbane rallied again, had a chance to seal it with two minutes to play but his reviewed set shot was shown to have missed.
Brisbane then shovelled the ball forward, Zac Bailey marking and sending the ball into the goal square.
Richmond's spoil bounced directly into Daniher's path, the lanky forward getting a boot to it for a two-point lead with just over a minute to go.
Lachie Neale (39 disposals, 21 contested possessions, 15 clearances) then made a crucial tackle to complete an incredible game and seal the ball in for the final seconds.
Richmond coach Damien Hardwick said fundamental errors had cost them.
"It summed up our year, to be fair. In the fight every game ... but the fact of the matter is the things that haunted us throughout the year haunted us again tonight."
Hugh McCluggage was impressive for the Lions while Dan McStay was a surprise performer when thrust into the ruck and three-goal Charlie Cameron's workrate was huge.
Jack Riewoldt kicked two goals from deep in the pocket in the final quarter to put his side back in front while Marlion Pickett and Trent Cotchin were solid.
In his return from injury Dustin Martin had 15 touches and kicked a first-quarter goal.
Prestia was asserting his influence when subbed with a hamstring issue, 18-year-old Darcy Wilmot kicking truly on debut for Brisbane then Zac Bailey running into an open goal to give the Lions a seven-point lead.
But, in just six kicks, Richmond scored the next three goals in a flash, Jack Ross's effort pushing them 11 clear.
Down by 16, Cameron streaked into the goal square to offer Brisbane life before Deven Robertson and Daniher split Tyler Sonsie's major to make it a five-point game at the break.
It was Cameron again just seconds into the final term, his snap pushing Brisbane ahead by one.
Both teams missed kickable set shots before McCarthy's mark 25 metres out, directly in front of goal was denied for a push off the ball.
Daniel Rich was then pinged for running too far as Brisbane rebounded again.
Tom Lynch marked but, with two minutes to play, his goal was reversed on review as it sailed high over the upright.
It was the break Brisbane needed as they got one to go their way after two finals losses by less than a goal in the last three seasons.
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