Lewis Alessandra ensured the Cobblers’ away-day troubles continued with a 90th-minute winner for Plymouth Argyle as the Cobblers hit rock bottom at Home Park.
Neither side made many contributions of attacking note and Town looked to have done enough to secure a rare clean sheet and away point when the game entered injury time.
But Alessandra swooped to make it a ninth defeat of the campaign for Aidy Boothroyd’s men and ensure they drop to the bottom of Sky Bet League Two after Accrington’s 1-1 draw with Wycombe.
Darren Carter had both of the game’s first attacking forays, winning a corner in the opening five minutes and hitting a shot over the bar shortly afterwards as both teams started at a low tempo.
The game sparked into life a quarter of the way through, Curtis Nelson heading Chris Hackett’s dangerous cross against his own post.
It was an interception Nelson had to make, with Luke Norris lurking behind him for what would have been a simple tap-in.
Former Sixfields loanee Jamie Reckord drew a good save from Matt Duke with an angled drive as Plymouth attempted to seize the initiative.
Mathias Doumbe, another player lining up against a former club, glanced a header wide from a Carter corner in the closing stages of the first half.
The theme continued as Guy Branston allowed a long ball to bounce in his own half, Luke Norris robbing him of possession and driving a goalwards shot that Luke McCormick blocked to safety with both hands.
Norris then wriggled away from Branston to find space for another shot, although this one flew wide of the target.
Lewis Alessandra was threaded in by Reuben Reid but his effort lacked power and was held low by Duke.
The goalkeeper had to be at his best, though, to keep out a Reid attempt that came out of nowhere but required a strong intervention just after the hour mark.
Chris Hackett beat two players down the right and struck a left-footed shot wide of the post and then won a free-kick in a good area after a poor Branston challenge, although the ball in came to nothing.
Norris won a free-kick in a good area with a driving run but Carter drilled it straight into Plymouth’s defensive wall.
Alessandra failed to connect with a devillish Paul Hayes pass across the goal as Northamptonian hearts entered mouths, Duke making a good low save from the same player as the game entered its final minute.
A single point became zero when Reid threaded a pass behind the visiting defence for Alessandra to latch onto and sidefoot past Duke to settle the contest.
Plymouth: McCormick, Blanchard, Trotman, Branston, Berry, Hourihane, Nelson, Reckord, Reid, Allessandra, Boco
Subs: Young (for Branston 76), Hayes (for Boco 80), Harvey (for Reid 90+2)
Not used: Cole, Blackman, Bencherif, Gurrieri
Cobblers: Duke, Collins, Doumbe, Reid, Widdowson, Hackett, Carter, Morris, Ferdinand, Dallas, Norris
Subs not used: Demontagnac, Tozer, Deegan, Emerton, McNamara, Toney, Harriott
Away fans: 220