Roosters captain James Tedesco starred in a 22-0 onslaught during the first 20 minutes of the second half that proved enough to secure victory at Accor Stadium on Friday night.
The Roosters began clumsily and leaked three tries in the final 10 minutes but coach Trent Robinson was happy to take any win in the first hit-out without sidelined stars Sam Walker, Victor Radley and Brandon Smith.
"There's no concern. Just finish the regular season, believe in what we're capable of and get ready to go," he said.
"We're in a position that we want to be. We take a breath tonight and tomorrow morning and then get ready to create a game-plan and a fight for (finals) next week."
Rugby convert Mark Nawaqanitawase opened the scoring on debut but the Roosters repeatedly cost themselves with first-half errors, completing only four of their first 10 sets.
James Tedesco was a key contributor for the Roosters with two tries. (Dan Himbrechts/AAP PHOTOS)
Walker's replacement at halfback, Sandon Smith, put Sitili Tupouniua over to trigger the second-half blitz after a quiet first half.
Tedesco took it from there, his support running sealing a second-half try-scoring double.
The Roosters' win spares them a trip to Melbourne to face the Storm in a qualifying final but will only be enough to secure week one hosting rights if Penrith lose to Gold Coast on Saturday.
Aside from Tedesco, Luke Keary and Angus Crichton signalled their intentions to step up in the absence of the injured brigade this finals series.
Fetalaiga Pauga was an attacking force for the Roosters, with three tries. (Dan Himbrechts/AAP PHOTOS)
Keary's play-making was the difference between the sides in a 14-10 first half, while Crichton finished with 185 metres and put Tedesco in for his first try through the middle.
Crichton has a nervous wait for the match review committee's charge sheet but looks unlikely to be suspended for hitting Tallis Duncan in the throat while running the ball early.
The loss mercifully ends the Rabbitohs' season but the ongoing fall-out from Latrell Mitchell's white-powder controversy means the aftershocks of their worst campaign since 2006 could be felt into the off-season.
Club great Tom Burgess barged over for a late try in his last game for Souths, while fellow departing Rabbitoh Damien Cook landed two of three conversions while moonlighting as goalkicker.
"I was happy that we came back at the end because it could have got ugly and we didn't deserve that with the season we've had, with all the injuries and all the other stuff that we've been through," said Souths interim coach Ben Hornby.
Latrell Mitchell watched from the sidelines but is set to serve his suspension in 2025. (Dan Himbrechts/AAP PHOTOS)
Roosters winger Nawaqanitawase had a brilliant NRL debut only 40 days after playing rugby sevens for Australia at the Olympics, opening the scoring after leaping to catch Keary's crossfield kick.
He defused what could have been Souths' first try by grabbing Cody Walker's own chip one-handed and offloading to put the Roosters in position for a 40-metre tear downfield.
Back-up winger Fetailaga Pauga injured his right knee grounding the ball from Tedesco's grubber kick to complete a hat-trick and is likely to join the long list of injured Roosters.
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