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,...