David Lee's chances to stake a claim to become the club's next permanent manager were blown away within 45 first-half minutes as the visitors raced into a three-goal lead.
Ben Tozer gave the hosts hope but a crazy last ten minutes saw five goals, four for the visitors, to leave Northampton in 20th place in League Two.
Attention now turns to the hunt for Gary Johnson's permanent successor to stop the Cobblers season into a full-blown scrap against relegation out of the Football League.