Two goals in quick succession put Cobblers on their way at Sixfields but the Daggers had opportunities to make their mark before slipping to a third defeat on the bounce.
An own goal from Abu Ogogo gifted Cobblers a 36th-minute lead, with Sam Williams squandering a couple of good chances for the visitors either side of the opener before Chris Hackett quickly doubled Northampton's advantage.
Matt Saunders and Brian Woodall both went close for the Daggers before Kelvin Langmead put the result beyond doubt for Town seven minutes into the second half, with Scott Doe finally reduced the arrears in the 71st minute.
Boothroyd said: "We rode our luck and it was a very scruffy performance. Give credit to Dagenham, they came to try and stop us playing but we got the goals at the right time.
"Dagenham gave us a lot of problems and their set-play was a cause for concern in the second half.
"We looked ring-rusty because of the lay-off, having two games postponed. But you are never going to play good football every week of the season, with the amount of changes, injuries and the weather.
"It turned out to be a comfortable victory in the end but now we need to get some consistency back into our games.
"The result has given us the platform to push on for the play-offs. We've got games in hand but we're going to be playing against teams around us now."