The Giants held a six-point lead at halftime, but their tsunami style swamped Brisbane in the third quarter, outscoring the Lions 14.2 to 0.3 on their way to a 26.10 (166) to 13.10 (88) win at Engie Stadium on Sunday.
The onslaught eclipsed the 13.4 Essendon kicked in the third term against Footscray in 1982, and was the fourth-highest scoring quarter in VFL/AFL history.
They also registered their biggest ever score, going past the 162 points they posted against Essendon in 2023.
Captain Toby Greene kicked five goals, four of them in the third quarter, and Jake Stringer pitched in with a handful of his own.
Max Gruzewski and Aaron Cadman scored three each.
Brisbane kicked the first four goals of the final quarter, but GWS booted the next three.
Making the Giants' feat even more remarkable was the fact that their injury woes continued to mount.
They suffered a blow before the match when veteran Lachie Whitfield was ruled out with hamstring awareness and was replaced by Harry Oliver.
The Giants then lost key defender Jack Buckley to a hamstring issue in the first quarter.
Lachie Neale gathered a team-high 32 touches for Brisbane, and Cam Rayner and Kai Lohmann each kicked three goals for the Lions.
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