Little more than a week after guiding Souths to a remarkable come-from-behind victory over the Sydney Roosters, Mitchell was quiet for much of Saturday afternoon as he filled in for the injured Cody Walker in the No.6 jersey in Perth.
While he set up tries for Euan Aitken and Jye Gray in brief moments of spark, Mitchell - in just his fifth NRL start as a five-eighth - was mostly happy to sit back and kick long on the fifth tackle.
Mitchell had just two runs throughout the 80 minutes at Optus Stadium.
It was in stark contrast to North Queensland No.6 Tom Dearden, who was a constant menace to the Souths defence.
The game was tied 10-10 heading into the final 20 minutes when Dearden slalomed across the field to set up rising star Jaxon Purdue.
Centre Purdue added a second try in the 67th minute to take the game beyond Souths.
The victory gives Todd Payten's side three straight wins heading into a bye round after starting 2025 with three consecutive defeats.
Injury-hit Souths, who boast a 4-2 start and face undefeated Canterbury on Good Friday, could have more personnel concerns ahead with Jack Wighton placed on report for a hip-drop tackle and prop Sean Keppie sinbinned for a high shot.
Mitchell had helped open the scoring when he sent South Sydney debutant Aitken in on a short ball in the 21st minute, before the Cowboys hit back via Murray Taulagi to claim a 6-4 halftime lead.
Jai Arrow crashed over early in the second half to put Souths back in front.
Wighton was placed on report for bringing down Scott Drinkwater with a hip-drop tackle in the 55th minute and on the ensuing set, Sam McIntyre dived on a Reece Robson grubberkick to the in-goal to tie the game 10-10.
Purdue then added his double, taking his tally to the season to five tries.
Mitchell chimed into the attack to set up Gray and make it a one score game with 10 minutes left.
But Keppie's high shot gave Drinkwater the chance to kick an easy penalty that sealed victory for the Cowboys.
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