With rookie halfback Lachlan Ilias finding his feet and gun No.1 Latrell Mitchell digging deep into his bag of tricks the Rabbitohs turned a 12-6 half-time lead into a comprehensive win.
With so much at stake the Rabbitohs charged out of the blocks with skipper Cameron Murray setting the tone with a try in the ninth minute.
The Roosters then invited their arch-rivals to double the lead with an error from a tap restart and Alex Johnston obliged with the 138th try of his career.
Roosters centre Joey Manu had raced up and taken a quick tap and passed to James Tedesco who tried to find Billy Smith but the ball went astray, Murray scooped it up and found Johnston for an easy stroll to the corner.
Some brilliant lead-up work by Manu set Tedesco up for a try in the 25th minute and the Roosters were back in at 12-6.
That's how it stayed until the break but the second half was barely a minute old when the Roosters got back to 12-10 through a sweet stepping try to Manu after the Rabbitoh George Burgess had coughed up possession in the opening set.
Ilias then played a leading role in Cody Walker's first try of the year and the Rabbitohs were up by eight.
Mitchell looked to have answered Manu's try soon after when he regathered a Johnston grubber and planted the ball down but replays showed the winger had dropped the ball before it made contact with his foot.
With 20 minutes remaining the Rabbitohs had a second try disallowed when Keaon Koloamatangi was ruled to have lost the ball and failed to regrip it before grounding after storming over from dummy half.
Not to be denied a second time, Koloamatangi took a pass from Damien Cook close to the line in the 64th minute and left Sitili Tupouniua in his wake to grab the try that took the Bunnies out to a 14-point lead with Mitchell's conversion.
Mitchell then put the icing on the Rabbitohs' first win of the season when he streaked away down the right touchline after a Roosters turnover on halfway was seized upon by Jaxson Paulo.
Daniel Tupou grabbed a consolation try for the Roosters but the night belonged to the Rabbitohs and their coach Jason Demetriou, who tasted his first win as a head coach.