Sharks halves Braydon Trindall and Nicho Hynes outplayed opposite pairing Thomas Duffy and Ben Hunt at Suncorp Stadium on Saturday night.
Hynes' running game was decisive and penetrating, while Trindall came up with nice touches at the right time, including two massive defensive plays to save tries and the final match-winning four-pointer.
Sharks coach Craig Fitzgibbon said it was the way the pair "knuckled down" rather than their flair that was decisive.
"I just gave them a wrap," he said.
"The number of supports they had tonight would have been probably season-high.You earn what you get and I thought they worked really hard off the ball for the team."
The Broncos have the most consecutive losses as defending premiers since Western Suburbs lost nine on the trot in 1953.
Unless Brisbane can beat Penrith away after next week's bye, they will join the Magpies in ignominy.
No side in the compulsory grand final era, since 1954, have lost eight matches in a row and made the finals.
The Broncos, 15th on 14 points, are eight points outside the top eight.
Maguire said he would have "pretty well everyone" back for the Panthers clash and that he believed they could win all their remaining games.
"Why not? I have got a lot of belief in the team and the group," he said.
"A bit of attention to detail cost us, but the effort from the players was excellent."
Stand-in captain Kotoni Staggs said "the two months of footy we have left could be the best two months of our lives" and backed up his coach.
The Sharks, still in the hunt for a top-four spot, scored first when Broncos winger Grant Anderson offloaded into the arms of Cronulla second-rower Billy Burns. Quick hands followed and Katoa scored in the corner.
Katoa had his second with a determined chase of a silky chip by Hynes.
Brisbane's lack of commitment in the chase was evident by the lacklustre effort by centre Gehamat Shibasaki to get back.
The incumbent Test centre appeared to be labouring on his return from a knee injury and was defensively off the pace.
The Broncos made errors, gave away penalties and only stayed in the match because Cronulla had their own discipline issues.
Brisbane gave NRL debuts to forwards Luke Gale and Joshua Coric off the bench.
Burleigh Bears prop Gale, 26, came up with a quick play-the-ball near the line and hooker Cory Paix burrowed over.
Katoa notched his hat-trick in the 56th minute after a visionary pass by five-eighth Trindall, before Hynes put fullback Will Kennedy through to make it 22-6.
Duffy set up fullback Hayze Perham for a try with a grubber, then Perham threw a magnificent cutout pass for Deine Mariner to score in the corner and give the hosts hope.
Trindall then swooped to snaffle an intercept and race 70m to seal the win.
The Broncos lost second-rower Brendan Piakura in the first half to a head knock after he copped a high shot.
The hosts had lock Xavier Willison cleared to play by the NRL after failing a category two HIA last week and he delivered a powerhouse display with and without the ball in front of Broncos prop Payne Haas, who travelled up from NSW camp.
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