It was a disappointing performance from Jon Brady’s men, who never truly got to grips with an impressive home team.
Vale were full of running, energy and attacking invention, pinging the ball around with confidence, with Brady admitting his team was ‘suffocated’.
Alfie Devine, Oliver Arblaster and the impressive Funso Ojo were at the heart everything the home side did, and although the Cobblers defended well and limited the amount of clear-cut chances, they were eventually worn down.
Substitute Ben Garrity was the man to break the deadlock, firing home a 20-yard strike five minutes from time.
Town were left to rue Sam Hoskins passing up their best chance just a matter of minutes earlier, but in truth the home side deserved their victory.
Here are our player ratings from an off-day at Vale Park...
9. Kieron Bowie
Started wide right and was the Cobblers' liveliest attacker in the first half. Bowie had the team's shot on target, which was well saved by Vale keeper Connor Ripley. Bit of a surprise to see him hooked at the break... 6 Photo: Pete Norton
10. Sam Hoskins
So often the Cobblers' goal hero, Hoskins had the chance to do it again at 0-0 as the clock hit 75 minutes - but he sidefooted his effort from eight yards over the bar. Had to hit the target. Ran his socks off as you'd expect, but another not at his best... 6 Photo: Pete Norton
11. Louis Appere
Did his best to have some sort of impact, and like the rest of his team-mates he put a shift in, but was starved of decent possession. Taken off at half-time... 5 Photo: Pete Norton
12. Manny Monthé
Brought on as a third central defender at the break, the former Walsall man had a solid second half. Part of a good rearguard effort... 6 Photo: Pete Norton