An early goal from former Cobblers loanee Danny East was enough to secure safety for the South Coast side and ensure that Northampton stay in the bottom two places of the Football League with two matches remaining of the season.
Manager Chris Wilder will see the game as a big opportunity missed as Bristol Rovers and Wycombe Wanderers both lost. All three sides remain locked on 47 points but goal difference keeps Town in the relegation zone.
Wycombe and Bristol Rovers meet next Saturday in a huge game at Adams Park. Northampton travel to face a Dagenham & Redbridge side who have little to play for.
It promises to be the pivotal weekend of the fight for survival and assistant manager Alan Knill said afterwards: "I'm confident that if we play like that in our next two games, we’ll stay up."