Competition heavyweights Melbourne rebounded after last week's heavy loss to take a tight AAMI Park win 24-16 in a sell-out match in wet conditions on Anzac Day.
Mitchell - who faced five charges last season - was sent to the sin-bin and put on report in the 50th minute for an alleged high shot on Sua Fa'alogo, with the Melbourne winger then failing a HIA.
While Souths have still never tasted victory south of the border, they delivered a much-improved effort on their shut-out by Canterbury last round.
The teams were locked at 10-10 at halftime, which showed Souths' effort given they only had 43 per cent of possession and 34 per cent of territory.
An error by Campbell Graham from the second half kick-off gave the Storm possession, and second-rower Eli Katoa plucked a Jahrome Hughes kick out of the air to score three minutes into the second half.
That lead went out to 18-10 when Ryan Papenhuyzen kicked a penalty following Mitchell's sin-binning.
Starting at his preferred fullback for the first time this season and captaining in the absence of injured five-eighth Cody Walker, Mitchell otherwise had a solid game.
Rabbitohs centre Jack Wighton bagged two tries while youngster Jye Gray, starting at halfback, was also a stand-out, with a couple of try-saving tackles.
Gray was involved in a bizarre incident with eight minutes remaining when he made a break and kicked ahead but collided with Papenhuyzen.
The Storm fullback challenged the decision but the bunker denied the challenge and also ruled it was a professional foul with Papenhuyzen spending the remainder of the match in the sin-bin.
While that gave Souths a sniff, the home side had built a 14-point lead courtesy of a 66th minute try to Tyran Wishart, with the Storm able to send the ball wide before Nick Meaney turned it back inside to his teammate.
Wighton got his second with three minutes remaining and while his team kept pressing, the margin proved too big to peg back, consigning Souths to their third straight loss.
