The diamonds prevailed.
The Broncos will have to beat their bogey side Melbourne in Brisbane on Thursday night to retain their fourth-placed position for the finals.
And they will need to be much better than they were on Saturday night in Townsville where errors and defensive lapses proved costly.
Walsh had five line-break assists, two try assists, a try and five errors. The good things outweighed the bad but against the top teams the Broncos will need to cut down on the mistakes, which were plentiful.
Brisbane coach Michael Maguire gave his side a spray at halftime, despite leading 22-18. The performance , particularly defensively, was not of finals standard.
The Cowboys received top-notch displays from fullback Scott Drinkwater, half Tom Dearden and props Jason Taumalolo and Jordan McLean but overall were far too loose.
Former Melbourne premiership winner McLean played his final match before retirement.
Broncos centre Gehamat Shibasaki scored a double, both off Walsh passes.
The turning point of the match came just before hafltime when Walsh started and finished a 75m long-range effort.
North Queensland five-eighth Jake Clifford gave his side every chance with a stellar performance.
Brisbane had more firepower and class overall to prevail.
Cowboys winger Braidon Burns was sin-binned for contacting the legs of Walsh as he kicked in the first half. Halfback Ben Hunt put centre Kotoni Staggs in with a slick short ball and it was 12-0.
A man down, the brilliance of Drinkwater created for winger Semi Valemei to score before hooker Reece Robson snuck over from close range to level.
Clifford then gave the Cowboys the lead.
Fill-in five-eighth Billy Walters threw a 20m pass for Broncos winger Josiah Karapani to level at 18-all.
Walsh then broke the game open just before the break with a looping pass.
Valemei swooped on a Walsh cutout pass after halftime to put the Cowboys ahead with his second try.
"It is my favourite play. I have just got to execute," Walsh told Fox Sports after the match.
Walsh responded to the Valemei effort by putting Shibasaki over for his second with a brilliant pass. The Walsh to Shibasaki partnership again delivered for Walters to score.
"I'm glad we got the win. We knew the Cowboys were going to come out firing," Walsh told Fox Sports.
"It is always an awesome challenge going up against them in Townsville."
Walsh has stepped up in the absence of injured skipper Adam Reynolds and five-eighth Ezra Mam as the Broncos won their ninth game from the last 11.
Coach Michael Maguire said the win was far from impressive.
"We've got a little bit to work on. I saw patches there that represented how we are growing ... but we still aren't satisfied with how we played," he said.Prop Payne Haas, who was outstanding, was one of several Broncos players who recovered from illness to take the field..North Queensland have the bye in the final round next week and will not play finals.
"I'm proud of the effort but it sums up our year … not good enough for the 80 minutes," coach Todd Payten said.
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