The Southern forward pack took control in the final 20 minutes to grind out a 21-13 victory over Pirates at Bathgate Park.
Southern stole an early advantage through a fortuitous intercept try to Tom Franklin and the early sinbinning of Shane Parata.
But a competitive Pirates side refused to yield under pressure, dominating territory and possession for the remainder of the first half.
Within minutes of the second spell, Pirates had drawn level at 13-13, through tries to Jake Maiono and Craig Sneddon.
Southern rang the changes for the final quarter and the game turned.
Pirates became starved of ball and Southern began to dominate by keeping the ball in its forwards, eventually adding points through a Bryce Hosie penalty and a Warren Moffat try.
Southern's tight five, particularly front-rowers Moffat, Johnny Mason and Mike Mata'afa, worked tirelessly in conjunction with the loose forwards, complementing a solid defensive screen in the backs.
Flanker Franklin was outstanding around the park and responsible for a lot of Southern's go-forward.
For Pirates, it was a game that was there for the taking until the final quarter.
Garth Swan, in his 100th premier match for Pirates, was impressive on the openside flank, as was blindside Josh Clark. Lock Brad Ross proved an imposing force, particularly at the lineout.
Southern 21 (Tom Franklin, Warren Moffat tries; Bryce Hosie con, 3 pen)
Pirates 13 (Jake Maiono, Craig Sneddon tries; Sneddon pen)
Halftime: 13-8.
