AFC Wimbledon boss Terry Brown found few positives after seeing his slip to their third straight defeat on the road.
A 2-0 reverse to Northampton means the Dons have conceded 13 goals in those three away games, with Alex Nicholls and Chris Hackett on target in the second half at Sixfields.
Cobblers broke the deadlock on the hour mark. Substitute Adebayo Akinfenwa made an instant impact as he set up Nicholls, who raced into the box and beat Mikhael Jaimez-Ruiz for his fifth goal of the season.
Hackett doubled Cobblers' advantage with a superb solo effort in the 72nd minute, picking the ball up 40 yards out and sprinting clear before finding the net.
Brown said: "I was pleased with the first-half performance and we started the second half brightly. We were looking to go up a gear but the first goal killed us.
"Both goals were dire from a defensive point of view, we tried to nick the ball from Adebayo Akinfenwa and didn't track the winger for the first goal, and both defenders got caught square for the second goal instead of one dropping off.
"Northampton are a good team and created a lot more chances than us but we had a few and had we stuck one away it might have made a difference."
Northampton boss Aidy Boothroyd was equally delighted with the clean sheet as he was with his side's three points.
He said: "We knew it was going to be a tough game even with the goals they had conceded in their previous away games because they looked good in their game at Southend.
"If you're going to be successful you've got to be persistent and we certainly were that. The clean sheet is the most important thing for me because we're always going to score goals with the team we have and what we can bring into a game from the bench."