Harry Anderson scored the only goal of the game after 38 seconds, collecting a short back pass from Fraser Horsfall and firing home from a tight angle.
Town battled hard to get back into the game, and went on to hit the woodwork twice, but couldn't find an equaliser.
Here are our player ratings from Sixfields.
9. Paul Lewis
The attacking midfielder came closest to levelling the match for the Cobblers when his volley was superbly saved by visiting keeper James Belshaw. Tried to link play, but along with most others, struggled... 5 Photo: Pete Norton
10. Sam Hoskins
Hoskins can't have had many quieter matches in a Cobblers shirt. As always, he put in maximum effort, but the game seemed to pass him by. Did send in good free-kick for Jon Guthrie's first-half headed chance... 5 Photo: Pete Norton
11. Louis Appere
Nobody can question Appere's effort, commitment or willingness to run himself into the ground, but the lone striker never got a sniff of a chance the whole game, and never looked like scoring... 5 Photo: Pete Norton
12. Peter Abimbola
The 18-year-old was thrown in at the deep end for his League debut after just 19 minutes, and acquitted himself really well before being substituted for tactical reasons on 72 minutes. A real positive on a disappointing day... 6 Photo: Pete Norton