Brisbane whiz kid Reece Walsh won the battle of the fullbacks with Latrell Mitchell in a 28-18 win over an error-riddled South Sydney.
Rabbitohs coach Jason Demetriou tagged his side's display "a horror show".
Walsh scored two tries at Suncorp Stadium in front of 35,507 fans on Thursday night, the second after a Mitchell blunder when he failed to gather an in-field kick by Broncos winger Jesse Arthars.
Broncos skipper Adam Reynolds battled through a recurrence of a right knee injury before leaving the field in the 70th minute.
"It stirred up what was already there and is pretty sore. I'll get another scan and see how it is," Reynolds said, as he races the clock to be fit for next week's clash with Penrith.
Apart from a six-minute spurt after half-time where bench utility Siliva Havili scored a try and set one up, the Rabbitohs were diabolical.
The Broncos led 12-0 at the break after both sides bumbled and fumbled their way through 40 excruciating minutes for their respective coaches.
The Rabbitohs were the worst offenders, completing just 10 of 20 sets.
They made a laundry list of elementary errors, including losing a scrum when they had the feed.
"I couldn't fault our defensive effort and resolve, but we are just shooting ourselves in the foot … whether we can't feed the scrum properly, first tackle errors or kicking into our own player or penalties for blocking," Demetriou said.
"It was a horror show."
After the Havili heroics, the Rabbitohs went back to their first-half ways.
Walsh and centres Selwyn Cobbo and Kotoni Staggs razzled and dazzled after Broncos forward leaders Pat Carrigan and Payne Haas dominated.
Two pieces of brilliance by Reynolds and Walsh lit up the half.
Reynolds, up against his former club, slid a masterful grubber kick through for winger Deine Mariner to score in the 18th minute.
Walsh made two handling errors early, but he didn't let that dent his confidence.
Instead, the talismanic No.1 stepped and weaved his way past six Rabbitohs defenders to score with blistering speed.
Hooker Damien Cook was sin-binned in the 29th minute and the Broncos were unable to make the visitors pay through their own mistakes.
Forward Kobe Hetherington muffed the best chance when he dropped the ball with the line wide open after being put through a hole by Carrigan.
Havili crashed through in the 43rd minute, then three minutes later put Davvy Moale over under the sticks to make it 12-12.
It was Walsh who stepped up when the match was on the line, not Mitchell, who scored a consolation try.
"In games like this where it's pretty tight, you need those (brilliant) guys and Reece is one," Broncos coach Kevin Walters said.
"It was a good performance from him.
"It was an ugly game. As a team we aren't quite nailing it, but you need to win those games at this time of the year."
Walsh and Cobbo combined beautifully to put Arthars over in the corner, before the Brisbane custodian sealed the deal with his second try.
Mariner iced the win with a brilliant chip and chase for his second try.
The Broncos' young guns were superb, with second-rower Brendan Piakura smashing opposite Cameron Murray on several occasions.
The hosts were far from perfect, but the Rabbitohs are 0-2 and look set for a long season.
Broncos five-eighth Ezra Mam, in his first game after Spencer Leniu's racial slur, almost scored from a grubber and had a sound game.
