Adam Birchall scored the only goal as Dartford secured their fourth victory of the season at Southport's expense.
The visitors struck the woodwork early on through Jamie Milligan's free-kick.
But the decisive strike came for Dartford midway through the first half as Birchall converted from Lee Noble's in-swinging corner.
Max Cornhill missed the chance for a second and Chris Almond was off target at the other end for Southport, who suffered their sixth league defeat.
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