It might all have been different had Clive Platt managed to guide a free header on target for the visitors in only the second minute, but the ball dropped wide.
The game exploded into life on 31 minutes as Ben Hutchinson curled a perfect 25-yard free-kick from a central position over the wall and into the top left corner.
The Cobblers were picking the ball out of the net again soon after as Ryan Tafazolli set up Sam Clucas for a low finish that managed to find its way under the keeper's dive, his fourth in four games.
Right on half-time, home keeper Alan Marriott preserved the two-goal cushion with a fine one-handed save to keep out Darren Carter's well-struck free-kick.
The visitors had three chances in a row on the hour, but Marriott beat away a Carter free-kick and Ian Morris' follow-up before Jacob Blyth headed over.
Instead, it was 3-0 soon after the hour-mark as debutant Mathias Kouo-Doumbe sliced Tafazolli's long ball forward up and over his own stranded keeper from 20 yards.
On 71 minutes, Marriott's legs denied Blyth in a one-on-one and, as the ball still travelled towards goal, James Jennings headed off the line.
The last kick of the game saw Carter hit a powerful shot against a post as the visitors' luck stayed firmly out.