Town were a pale imitation of their usual energetic and vibrant selves and they could have no complaints as previously out-of-form Barrow ended their three-game losing run with alarming ease.
Aaron Amadi-Holloway was the match-winner, heading home just after half-time, and despite having nearly the whole of the second-half to respond, Northampton were unable to create anything.
The defeat is not the end of the world for Town, who remain fifth, but their performance was desperately poor, as bad as anything they have served up this season and certainly not that of promotion contenders.
The Cobblers made one change from the team that beat Salford on Saturday as Josh Eppiah made his full debut for the club, replacing Idris Kanu.
Bez Lubala was named on the bench but fellow deadline day arrival Louis Appere had not signed in time to make the squad.
Eppiah was almost rewarded for his relentless pressing five minutes in but the ball would just not fall for him after he had closed down visiting goalkeeper Paul Farman.
Despite that scare though, Barrow had made a sharp start to the contest with Remeao Hutton's shot blocked and Luke James flicking a cross into the side-netting.
Mitch Pinnock slashed a half chance high and wide but Barrow were edging the tactical battle with their wing-back system and continued to have the better of it.
The improvement from Northampton was gradual but they did get better and again Pinnock had a crack, this time hitting the target but Farman was down to make the stop.
Sam Hoskins also forced Farman into action but again it was a comfortable save and those were the only meaningful opportunities created by Town in the first-half.
And the hosts were punished for their lacklustre performance six minutes into the second-half when John Rooney and Anthony Driscoll-Glennon linked up on the left and the latter's cross was slotted in by Amadi-Holloway.
That should have lifted Cobblers from their collective slumber but it failed to do so, leaving Jon Brady to turn to his bench and send on Lubala for a debut, as well as Danny Rose.
Again, though, there was just no spark or quality or urgency and Cobblers continued to sleepwalk their way to a dispiriting home defeat.
Idris Kanu was also introduced and the hosts were even given eight minutes of stoppage-time to find a leveller, but not once did they seriously test Farman and the full-time whistle duly completed a thoroughly disappointing night.
Cobblers: Roberts, McGowan, Horsfall (c), Guthrie, Koiki, McWilliams, Sowerby, Lewis (Kanu 76), Hoskins, Pinnock (Lubala 67), Eppiah (Rose 67)
Subs not used: Maxted, Harriman, Mills, Magloire
Barrow: Farman, Brown, Brough, Taylor, Beadling, Driscoll-Glennon, Hutton, Banks (c), James (Kay 75) (Jones 90), Rooney, Amadi-Holloway (Harris 68)
Subs not used: White, Wakeling, Williams
Referee: Lee Swabey
Barrow fans: 151