Walsh set up two tries in the first half at Sunshine Coast Stadium with passing wizardry and then put his foot down after the break to leave the Rabbitohs' defenders clutching at thin air in a scintillating 40-metre sprint to the tryline.
Broncos coach Kevin Walters was blown away by 21-year-old Walsh's return after a three-week suspension. There was no rust.
"The message this week, particularly because he'd missed the last three, was, 'Play with what your great assets are'," Walters said.
"That's his running game first up, and then pass after that … but he managed to find both on a couple of occasions. So he is a bit ahead of even the coaching staff."
The Broncos are now on 32 points and on top of the NRL ladder at least until Penrith host Canterbury on Sunday.
The Rabbitohs are eighth on 24 points but are no certainties of even staying in the finals hunt if they keep playing like they did on Friday.
They have now lost six of their last eight games and have fallen off a cliff defensively.
Constant errors with the football and a lack of discipline without it are haunting the Rabbitohs.
"Bitterly disappointed," Rabbitohs coach Jason Demetriou said of his side's performance.
"I don't think we were up for the physicality. It was pretty embarrassing by the end."
Souths led 14-12 at the break after a first half in which neither side could hang on to the ball.
Broncos prop Martin Taupau was sin-binned and put on report in the 13th minute for lifting his leg straight into Rabbitohs centre Campbell Graham while running the ball.
It was individual brilliance that led to points in the opening half.
Walsh spiralled a pass for a Kotoni Staggs try and then sent winger Selwyn Cobbo over with a sensational cut-out.
The Rabbitohs put the foot down in the sixth minute with a classic left-side play.
Five-eighth Cody Walker and fullback Blake Taaffe combined to send winger Alex Johnston over for his 181st career try.
Time was up on the clock at the end of the first half when Graham crashed over from close range after a crafty pass by hooker Damien Cook to give the Rabbitohs the lead at the break.
The match was crying out for a gamebreaker and Wash put his hand up to be the man when, with breathtaking speed and evasion, he blitzed his way to a try and celebrated with a backwards somersault.
Giant Broncos prop Xavier Willison, a late inclusion on the bench after illness ruled out back-rower Brendan Piakura, then crashed over from close range to make it 24-14.
Staggs scored his second before Broncos winger Jesse Arthars was sin-binned for a high shot on Taaffe.
The Rabbitohs scored through Isaiah Tass out wide but when Brisbane skipper Adam Reynolds went in against his former club it was game over.
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