Adam Reynolds put the boot in for 40 minutes before Benji Marshall and Damien Cook ran the Rabbitohs to safety and a 26-12 triumph after a Sea Eagles boilover had loomed.
Reynolds only needed one half of football to kick South Sydney's one-year extension offer to the kerb, the pint-sized playmaker controlling the contest right up until he copped a head knock immediately after halftime.
The 30-year-old remains at loggerheads with Souths over his future beyond 2021, with the club yet to budge on the one-year deal that has Reynolds ready to hit the open market.
He put his wares well and truly on show with a superb opening half that featured a try, a 40-20 and general bombardment of Manly's makeshift fullback Dylan Walker.
But after a collision with Sea Eagle Sean Keppie the halfback's day was done as the Rabbitohs led 14-6, prompting Manly's move against the heavy pre-game favourites.
Match: Sea Eagles v Rabbitohs
Round 2 -
Venue: 4 Pines Park, Sydney
"He played well but he had a lot of mates playing pretty good for us as well, but he certainly stepped up for us," Bennett said simply of Reynolds' early masterclass, adding that he expected him to pass HIA protocols to be fit for next week's grudge match with the Roosters.
Asked if the sodden conditions suited Reynolds to a tee, Bennett said: "I don't think so, it's just what you gotta play.
"That's the conditions on the day, he's played over 200 games so he's played in all types of conditions. He was just on his game, that was the key part."
Marshall magic leads to Cook try
Big men Marty Taupau and Taniela Paseka combined at the line for the former to bag a rare four-pointer that reduced Manly's deficit to just two with 20 minutes to play.
But with Marshall slotting in as Reynolds' replacement, the 36-year-old split the Sea Eagles up the middle soon after.
Once the oldest legs in the NRL were into gear and into the backfield, Marshall produced one of the vintage flick passes kids have been mimicking for almost two decades now.
"I was really pleased with Benji's contribution after we lost Adam," Bennett said.
"He came on at halftime because we lost Jaxson Paulo (to concussion), but he was a good influence on the team, Benji."
From the next play it was Cook taking on the line from dummy-half and dummying his way over to give the Rabbitohs back their breathing room.
With Reynolds and winger Paulo both failing HIAs, Manly's Cade Cust also badly concussed and Andrew Davey suffering a suspected ACL rupture, a battle of attrition ensued as the rain belted down.
In the end South Sydney's early points proved enough. For Manly it was a sorely needed and much-welcomed improvement on last week's horror show against the Roosters.
Mitchell makes the metres then sets up Johnston
But they have still lost 10 of their past 11 games, seven of their past eight outings on home turf and have yet more additions to a bulging casualty ward.
“There are clutch moments in the game where we just have to be better than we currently are,” coach Des Hasler said.
“We need to keep mindful of that. The two points were there and we didn’t go on with it. We need to step up and fix that. It’s not going to get any easier, is it? Particularly with some of the injuries we picked up today.”
The Rabbitohs started their run through Walker in just the fourth minute, whose left-side raid featured a lightning tap-on from Mitchell before the pivot polished off the play for a 4-0 lead.
Reynolds gets to his own kick first
With Reynolds scoring from his own grubber and Davey already gone for the day, another Manly mauling loomed ominously after last week's thrashing from the Roosters.
But as the Sea Eagles defence held Daly Cherry-Evans eventually sparked his side.
The Manly No.7 made his own inroads with a sharp grubber and chase to rival Reynolds, with Mitchell sin-binned for clipping Cherry-Evans as he pursued his kick.
Lachlan Croker made short work of the 12-man defensive line, and should've thrown a dodgy Rolex in with the dummy he sold Mark Nicholls to make it 10-6.
That scoreline should've stayed as the players went to the break, but Dylan Walker's bizarre decision not to play at Reynolds' 40-20 gave South Sydney one last crack before the pause.
Mitchell duly scored from a pinballing Cody Walker punt. And after all the drama, casualties, and even more rain, Mitchell was in it again after Souths had put enough distance on the scoreboard.
His quick hands for Alex Johnston's last try bode well ahead of next week's showdown with the Roosters.
The scuffle he was right in the middle of at full-time, less so.
Players from both sides piled in and eventually Jaydn Su'A was sin-binned, with the entire incident placed on report for the match review committee to deal with.