Southport survived a late Forest Green fightback to hold on for the win.
Earl Davis put the visitors in front when he finished from Kevin Lee's header before James Rowe's thunderous effort rattled the bar for the hosts.
Karl Ledham's free-kick was headed in by Simon Grand before Shaun Whalley's superb 25-yard effort made it 3-0.
James Norwood hammered in a free-kick and Yan Klukowski headed home Keiron Forbes' cross in stoppage time but it was not enough for Rovers.
VIEWS FROM THE DRESSING ROOM
Forest Green Rovers manager Dave Hockaday told BBC Radio Gloucestershire:
"We weren't good enough today, they wanted it more than us and they worked harder than us.
"They came, they had a game plan and it worked for them.
"That's the first time this season that we didn't deserve anything from the game."