Fraser Hornfall's 82nd-minute strike condemned Newport to defeat at Northampton.
Northampton had the first attempt at goal in the second minute, but Shaun McWilliams could only hit a half-volley from a corner into the ground and over the bar.
County responded 10 minutes later when Aston Villa loanee Finn Azaz had a fierce strike from a tight angle beaten away by Liam Roberts in the Northampton goal.
Just after the 20-minute mark, Roberts needed to make a top save again to deny Dom Telford's volley and Northampton cleared the resulting corner.
The hosts came closest to breaking the deadlock, but Sam Hoskins' poked effort past Nick Townsend was slid off the line by a superb recovery challenge by skipper Mickey Demetriou.
Louis Appere came close to making it 1-0 to the hosts soon after the restart, but he ballooned an effort over the bar with just Townsend to beat.
County's best chance of the game came 25 minutes from time, but League Two top scorer Telford was brilliantly denied by Roberts in a one-on-one battle after Telford was perfectly played in by a Finn Azaz through ball.
Northampton's best chance came four minutes later, but left-back Ali Koiki skied an effort over the bar after he was found at the back post by Mitch Pinnock's cross from the right.
The set-piece specialists got the goal they way they are so used to, as captain Horsfall diverted a corner from the right in from close range with eight minutes to go.
Northampton Town: Liam Roberts, Jon Guthrie, Fraser Horsfall (C), Sam Hoskins (Josh Eppiah '80), Paul Lewis, Beryly Lubala (Idris Kanu '58), Mitch Pinnock, Ali Koiki (Joseph Mills '87), Shaun McWilliams, Tyler Magloire, Louis Appere
Subs not used: Jonny Maxted, Michael Harriman, Scott Pollock, Danny Rose
Newport County: Nick Townsend, Cameron Norman, Josh Pask, Mickey Demetriou, Ryan Haynes, Scot Bennett, Robbie Willmott (Rob Street '83), Finn Azaz, Jake Cain (Oli Cooper '63), Courtney Baker-Richardson, Dom Telford
Subs not used: Joe Day, James Clarke, Matt Dolan, Aaron Lewis, James Waite