Forest Green suffered their third consecutive defeat with a goal coming in each half with Neil Grayson putting the ball in his own net and a last-minute strike by substitute Gary Bauress.
The visitors came close within two minutes when Peter Thomson's left-footed drive from just outside the area needed Rovers keeper Steve Perrin at full stretch to palm the ball behind for a Southport corner which came to nothing.
Southport however, did take the lead from a corner after 14 minutes when Dean Howell's cross into the box found Barry Jones, whose header deflected off Grayson into the left-hand corner of the net.
Forest Green's first real chance came after the half hour when Steve Jenkins found Alex Meechan on the left-hand side of the Southport penalty area and his low cross went straight across the face of goal invading both Rovers attack and Southport's defence.
After 36 minutes another chance came Rovers way. This time Meechan's cross from the right wing found Alex Sykes just inside the penalty area and his first time volley was well saved by Southport keeper Steve Dickinson.
Southport's new summer signing Mark Lloyd-Williams came close right on half time after picking up a long pass from Steve Jones only to see his low shot saved by Perrin.
Dickinson was required to make a save within minutes of the restart with Alan McLoughlin's 20-yard drive forcing the keeper to tip the ball over the crossbar.
Southport should have had a second after 54 minutes when a dangerous cross into the Forest Green penalty area found Williams at the back post but he headed wide from close range.
The visitors almost wrapped the game up five minutes from time when a misjudgement from the Rovers defence allowed Thomson to run through but Perrin's presence forced the striker out wide and his knock back found substitute Steve Whitehall whose strike forced Perrin to palm the ball wide.
The game was sealed in the last minute when Bauress who had just come on as a substitute picked up a loose clearance and with his first touch of the game fired the ball into the top right-hand corner