Harry Smith scored the only goal at the Fullicks Stadium right on the half-time whistle to stretch Invicta's lead at the top of the table to 14 points.
Third-placed Herne Bay were held to a 1-1 draw by mid-table Tooting & Mitcham United at Imperial Fields.
Sam Hasler gave Bay a great start with a goal inside nine minutes. But Jake Baxter eventually pulled the Terrors back into the game with 15 minutes remaining.
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