Southport further eased their Conference Premier relegation fears at the expense of Forest Green Rovers' play-off hopes.
Karl Ledsham superbly headed home Blackburn loan man John O'Sullivan's cross to set the Sandgrounders on their way four minutes into the second half.
James Norwood was close to levelling when he hit the bar with a 12-yard lob.
But O'Sullivan secured the victory with a 20-yard right-foot shot into the bottom corner from Ledsham's pass.
And Rovers goalkeeper Sam Russell had to make a string of fine saves to keep the score down.
John Coleman's Southport are now seven points clear of danger, while Rovers' first defeat in four matches leaves them three points adrift of the play-off zone.