NRL heavyweights Melbourne have suffered a fourth straight loss after being defeated 24-12 by South Sydney.

Melbourne's mid-season slump has shown no signs of ending after South Sydney inflicted a 24-12 defeat on the Storm at Accor Stadium.

The loss means that Craig Bellamy's side have dropped out of the NRL's top-four after suffering a fourth consecutive defeat for the first time since 2015.

And the master coach admits finding a way to arrest the slide isn't going to be easy.

"No, I'm not confident I can turn it around," said Bellamy, whose side drop down to fifth ahead of next Friday's trip to Auckland to face the Warriors.

"There's some stuff that you're not going to get away with at this level and you'll pay a price.

"If you keep making errors and you don't back it up with defence, you're going to lose the game and that's what happened tonight."

Souths' victory - their first over Melbourne since 2018 - was inspired by the try-scoring feats of winger Alex Johnston, who completed a brace either side of halftime and now has 13 tries in his past six games.

The Papua New Guinean international took his tally of career tries to 157 and is one score away from entering the top 10 of tryscorers in the history of the game in Australia.

Keaon Koloamatangi, Jaxson Paulo and Lachlan Ilias all joined Johnston in crossing the whitewash as Souths recorded their fourth straight win.

Koloamatangi got the Rabbitohs rolling with a first-minute try and no matter how hard Melbourne tried they quickly became the architects of their own downfall by coughing up the ball on a soggy Sydney night.

Nelson Asofa-Solomona, Harry Grant and Alec MacDonald were all guilty of clumsy ball handling and television cameras captured Bellamy in a state of rage in his coach's box.

"We've got guys with injuries, but at the end of the day, we've got guys in our team and we don't pick them up off the street," Bellamy said.

"They've been playing footy for a fair bit and they need to catch the ball, pass the ball and make their tackles."

Johnston scored his first after teaming up with Latrell Mitchell and the only time that Souths' defence relented in the first half, centre Marion Seve got the Storm on the board.

Seve cantered past Cody Walker from a scrum play to score from 50 metres out to cut the Bunnies' halftime lead to 10-6.

After the break, Mitchell set up Johnston in near identical fashion before Ilias backed up a bustling Koloamatangi to dot down.

Mitchell had a quiet night by his standards but the fullback nearly pulled off the play of the season when Souths were deep in their own territory on zero tackle and he kicked over the top for Johnston to chase.

Johnston beat all the Storm players to the ball and hacked ahead only to fumble in the in-goal.

Paulo extended Souths' lead soon after with Dean Ieremia offering Melbourne's only response with a little more than 20 minutes to go.

"The best thing about the game was we showed we can defend," said Souths coach Jason Demetriou, whose side moved up to sixth spot on the NRL table.

"It (defensive resolve) is a mindset and it's really hard to defend with that kind of resilience for 24 rounds and into a finals series.

"But I think the boys understand that's what we need to do to get where we want to go; we have got to have that resolve."