Aidy Boothroyd sent his side out looking for a third successive victory but goals in each half from McCombe and Rigg made it an uphill task.
Bayo Akinfenwa gave the 5,803 crowd hope with a goal ten minutes from time but a comeback proved beyond the Cobblers, who remain in the relegation zone.
An angry Boothroyd told the official club website afterwards that his side 'got what they deserved' from the game.
"In any fixture, at any level you can't only start playing with 15 minutes to go and that's what we did today."