The Dolphins were able to strike early, with Isaiya Katoa and Trai Fuller combining to send Jack Bostock over after 6 minutes. But Souths didn't take long to reply, and Jye Gray was awarded a penalty try when he dropped the ball over the line but was impeded on his chase by Fuller.
The Dolphins soon hit the front through a Tevita Pangai Junior barge over, but Connolly Lemuelu dropped the ball from the kickoff and Souths hit back through Jacob Gagai to make it 12-10.
The Phins were able to extend their lead not too long later through a great individual try by Herbie Farnworth. They had chances to add onto it even further as the first half ticked down, however great defence by Souths and some poor attacking execution kept the score 18-10 at the break.
It was a set piece that got the Dolphins across to start the second half, when Katoa grubbered in behind and Kodi Nikorima was the only man on the peninsula who saw it coming.
But Souths began to win back momentum, and a couple of quick tries from Gagai and Alex Johnston brought the game back to 24-18.
But just as the tide was turning, a penalty kick by Jack Wighton failed to find touch, and the Phins capitalised on the ensuing set when a Pangai Junior offload created a linebreak that concluded in Jake Averillo putting Sean O'Sullivan over the line.
Then they aced the set after points when Katoa put Bostock through the line, who duly found Fuller on the inside to put the Dolphins up 36-18.
Late tries by Johnston and Gagai threatened to bring the game close, but the Dolphins held on for a good win.
They didn't escape unscathed unfortunately, with Euan Aitken suffering a suspected ruptured pec while Kodi Nikorima succumbed to a shoulder injury. For Souths Davvy Moale had a late HIA and it's unclear whether or not he passed.