Corbett, McGrath and a Dunn own goal did the damage in the first half as the visitors belied their lowly league position to race into a three goal lead.
Ian Sampson will be able to draw some comfort from a second half fightback by his side which yielded goals from Johnson and Holt but in the final analysis will deem the game as yet another opportunity lost to kickstart a play-off push.
Reaction to follow on Cobblers Mad.