The Reds have all but secured a home final after defeating the Brumbies 24-22 in a classic at Suncorp Stadium.
Their' seventh-straight win this season and 10th consecutive at Suncorp Stadium came after a frantic five minutes of defence after they edged ahead for the first time in the 77th minute.
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The Reds went in without in-form Wallabies centre Hunter Paisami (calf), teenager Josh Flook given the task in the centres as coach Brad Thorn kept Petaia on the wing.
Led by an aggressive Rob Valetini, the Brumbies had the better of the early exchanges but Flook defended stoutly and was rewarded with a second-half try down the blindside that came from another clever O'Connor kick.
Wright had the immediate reply though as the Brumbies edged closer to their first win in Brisbane since 2015 - one that would have kept their own hopes of hosting the decider alive.
The visitors were clinical early, Folau Fainga'a tip-toeing inside the right touch line to score from a rolling maul before Tom Banks ran 70m from an O'Connor intercept.
The hosts earned back some ground and O'Connor kicked two penalties to peg back the margin before it looked as if 100-gamer Bryce Hegarty had put them within a point.
He chased a Hamish Stewart grubber 50m, his tackle on Andy Muirhead knocking the ball clear before the fullback got a hand on it.
The try was denied on review though, officials curiously judging Hegarty had knocked the ball forward while making the tackle.
They had other moments too but penalties spoiled them, Nic White nailing a 53m penalty for the 15-6 lead on the half-time buzzer.
Despite Brumbies captain Allan Alaalatoa's return, the Reds' scrum held firm though as they slowly pegged their way back.
This is where Petaia, who scored the late winner when the sides last played, pinned his ears back and nailed a 50-22 kick.
He then out-jumped Tom Banks to win a James O'Connor bomb, finding the turf to make it a four-point game.
O'Connor then kicked another penalty before Fraser McReight and Angus Scott-Young won a crucial turnover in front of their posts as the Brumbies sniffed a match-sealer.
Another scrum penalty then gave O'Connor the chance to kick for the lead from a slight angle 35m out and he made no mistake.
They then twice forced turnovers as the Brumbies probed either side of the full-time siren in another classic encounter between the sides.
REDS 24
TRIES: Flook, Petaia
CONS: O'Connor
PENS: O'Connor 4
BRUMBIES 22
TRIES: Fainga'a, Banks, Wright
CONS: Lolesio 2
PENS: White
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