Five-eighth Cody Walker was the mastermind behind the Bunnies' victory on Thursday night as Wayne Bennett's side (7-6) strengthened their bid for a top-eight spot.
Walker had four try-assists and Alex Johnston grabbed a quartet of tries as Souths snapped a three-game winless run.
But the story of the night will be Brisbane's nosediving form as they returned to Accor Stadium for the first time since Maguire engineered a drought-breaking premiership win nine months ago.
The Broncos began their losing run with defeats to top-four contenders in the Sydney Roosters, Manly and the Warriors.
But the last three weeks, where Maguire's men have been beaten by wooden spoon favourites St George Illawarra, struggling Gold Coast and an injury-depleted Rabbitohs side, have highlighted how far Brisbane have fallen.
"We're still well and truly alive and people will probably think I'm mad," Maguire said.
"I know I've got a number of guys not on the field at this present moment… but they'll all come back and there's a lot of quality there that I know that can come back into the team.
"We're probably in a bit of a tough hole at the moment and we all know what this team's capable of doing.
"We don't like going through it but it can also be the making of us."
The Broncos (5-9) are in danger of becoming the first reigning premiers to miss the finals in the following season since Wests Tigers finished outside the top eight in 2006.
And adding to Brisbane's woes, halfback Adam Reynolds (hamstring) and five-eighth Ezra Mam (shoulder) failed to see out the match.
On an emotional night, where both clubs united to celebrate the life of Jai Arrow following his diagnosis with motor neurone disease, Souths raced out to a 30-0 halftime lead through an Alex Johnston double and tries to Ed Kosi, Jamie Humphreys and David Fifita.Â
Josiah Karapani finally got the away side on the board in the 52nd minute, but there was no sense of fightback brewing.
Nothing summed up the Broncos' night more than Ben Hunt passing the ball into the back of Preston Riki when the forward was looking towards his own tryline shortly before Mam and Reynolds went off.
They just pulled a rabbit out of a hat! � #NRL pic.twitter.com/opO4nOzWFo— NRL (@NRL) June 11, 2026
Johnston crossed two more times in the final 20 minutes, while debutant John Radel also touched down to help Souths run up a big score.
"We're in pretty good place if we can just maintain the way we played tonight," Bennett said.Â
"We're capable of doing that, so that's our next challenge."Â
