After missing the first month of the season with injury, Mitchell stood tall to drag a depleted Rabbitohs side off the canvas and snatch a famous win at Accor Stadium on Friday night.
Souths played the final 30 minutes with just 14 fit players after five-eighth Cody Walker, halfback Jamie Humphreys and winger Mikaele Ravalawa hobbled off with hamstring issues.
But in front of a crowd of 22,114 - and as his Bunnies trailed 14-8 with little more than a quarter of an hour left - Mitchell rose to the occasion against his former club.
An audacious goalline drop-out from Mitchell bounced in Souths' favour and led to Jye Gray's try under the posts, which made it 14-14 in the 64th minute.
Mitchell, filling in at five-eighth after being named to start at centre, then produced the play of the game to condemn the Roosters to a 1-4 start.
Rather than set up for a field goal attempt, he ran to the left and hit winger Isaiah Tass with a perfect cut-out ball that zipped past three Roosters players.
Tass tip-toed down the touchline to score.
Mitchell converted to seal a Souths win that gives his side a 4-1 start under returning supercoach Wayne Bennett.
Humphreys' early exit led to Jayden Sullivan being thrown into the action after just five minutes but the playmaker's first act of note was a missed tackle on Roosters five-eighth Sandon Smith.
But Smiths' encouraging play was not helped by his halves partner Chad Townsend.
The veteran No.7 sent a kick out on the full, shanked a goalline drop-out into touch, and was penalised for a ball-strip penalty that led to Junior Tatola's 11th minute equaliser.
After having a try chalked off in the first half, Mitchell put Souths in front for an 8-6 halftime lead.
Mitchell kicked a penalty goal after James Tedesco was penalised - not sinbinned - for a high shot on Rabbitohs hooker Peter Mamouzelos.
When Walker didn't return in the second half the Roosters sensed blood, and with the Rabbitohs in a state of disarray, Tedesco was the spark for his side.
The fullback jinked out of dummy-half at a retreating defence in the 45th minute, flinging the ball wide for Billy Smith to finish in the left corner.
Ravalawa limped off soon afterwards and injury-hit Souths were barely holding it together when Dom Young crossed on the Roosters' right wing.
Jack Wighton was filling in as a winger for Souths, forwards Jai Arrow and Tallis Duncan were sharing centre duties, and Mitchell was trying to conjure some magic in Walker's five-eighth berth.
He did so courtesy of the dropout that looked like a mis-hit when the first bounce landed closer to Souths' tryline.
But the ball trickled back towards and over the 10m line.
Arrow was quickest to react and the Roosters' ill-discipline allowed Souths up the other end where Gray finished a Sullivan break..
Then the headline moment came with 10 minutes left as Tass touched down off a pinpoint pass that etched a new chapter in the storied career of Latrell Mitchell.
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