David Ball proved Northampton's undoing, creating one and scoring another as high-flying Fleetwood rallied to a 3-0 victory.
Uwe Rosler's men went into the game on a run of 16 unbeaten in League One.
But it was the Cobblers who made the early running and should have gone ahead.
Marc Richards got goalside of Cian Bolger, lofting a neat ball to Michael Smith who rattled the woodwork from barely five yards out.
Richards was involved again minutes later, Keshi Anderson wrong footing the Fleetwood back line, his skipper darting in to test Alex Cairns, the Fleetwood keeper diving to push the shot around the post.
Justin Edinburgh's side seemed determined to stamp their mark on the game, Michael Smith firing wide from close range as the high-flying hosts looked to be limping to the break.
But the game turned in a second when Adam Smith hesitated under pressure from Ball.
The Fleetwood striker's chip was never likely to find the net, Town needing Devante Cole to finish the job.
Darting behind Northampton lines he was denied at the first attempt but pounced on the rebound, finding the net from the tightest of angles.
Ball might easily have doubled Town's tally within minutes of the restart, another moment of uncertainty going unpunished as his shot slipped just wide of the back post.
Fleetwood did soon find their second, Bobby Grant skipping around two men and firing past Smith from the right of the six yard box.
A second goal in the space of four minutes ended any hopes of a Cobblers comeback, Ball this time the architect and scorer.
He made the most of David Buchanan's slip, racing in from the left and picking the moment to lift the ball over the advancing Adam Smith, the former Manchester City man deservedly bagging his 13th of the campaign.