It was not the most entertaining affair at Rodney Parade, and again goalscoring opportunities were at a premium, but Jon Guthrie's goal late in the first-half was all Town needed to take the points thanks to another terrific defensive performance.
The first-half contained very few chances - not for the first time this season - but Cobblers did well to hold off Newport's strong start and get their noses ahead through Guthrie's thumping finish.
The visitors then went into game management mode in the second period and bar a five-minute period when they were on the retreat, they limited last season's beaten play-off finalists to not a single clear-cut opportunity.
The clean sheet is Cobblers' fifth in seven games this season and the three points lift them to third in the table.
Jon Brady made three changes from the weekend as Jack Sowerby came in for his first league start of the season and Mitch Pinnock and Nicke Kabamba also returned.
Newport made the sharper start but Cobblers weathered the storm without any major alarm and gradually wrestled a foothold in the contest.
Town prevented the home side from finding any fluency in a scrappy and, at times, feisty first-half, and and they also carried the greater goal threat with Pinnock blazing well over and Danny Rose closed down just as he was about to pull the trigger.
There were very few clear chances but that changed right on the cusp of half-time and Northampton made it count.
A free-kick caused chaos in Newport's penalty box and the ball eventually fell kindly for Guthrie to smash home.
Jake Cain fired a free-kick wide for Newport soon after half-time and Robbie Willmott was twice off target from range, but otherwise the home side struggled to build any momentum.
And they were grateful for goalkeeper Joe Day not to fall further behind midway through the second-half when he reacted smartly to keep out Kabamba's header.
Cobblers managed the game well but began to sit off in the last 15 minutes which allowed Newport to create a head of steam and finally put some pressure on Liam Roberts' goal.
But the visiting goalkeeper was only called upon once and that was to keep out Cameron Norman's tame back-post header.
A remarkable 12 minutes of stoppage-time were added at the end following a serious injury to Newport's Scot Bennett but despite all that time, Newport continued to toil in attack.
Cobblers were superb again defensively and battled through all 12 of those minutes to record yet another clean sheet.
Newport: Day, Haynes, Demetriou (c), Farquharson, Norman, Bennett (Azaz 72), Livermore, Cain (Cooper 57), Collins (Ellison 57), Willmott, Abraham
Subs not used: Townsend, Clarke, Dolan, Lewis
Cobblers: Roberts, McGowan, Horsfall (c), Guthrie, Koiki, McWilliams, Sowerby (Connolly 88), Hoskins, Pinnock, Rose (Flores 85), Kabamba (Etete 85)
Subs not used: Maxted, Harriman, Pollock, Ashley-Seal
Referee: Craig Hicks
Cobblers fans: 161