Cambridge United inflicted more last-gasp agony on the Cobblers when David Amoo scored deep into injury-time to grab a 3-2 victory after a pulsating affair at the Abbey Stadium on Saturday.
Town twice led through goals from Aaron Pierre and Junior Morias in each half but, blighted by injuries, they surrendered the advantage on both occasions before being beaten with virtually the last kick of the game.
Pierre's thumping finish had given the visitors a surprise lead after United started firmly in the ascendancy but Jevani Brown produced a sublime effort in first-half injury-time to level things.
Junior Morias thumped Cobblers back in front straight after the restart before George Taft again equalised, and it would get better for United in injury-time thanks to Amoo's dramatic winner.
The Cobblers battled valiantly with a patched-up young team that included a midfield of teenagers Jay Williams and Scott Pollock but United utterly dominated the second-half and warranted the victory, leaving Town to contemplate a potentially tricky end to the season given they are now placed just six points above the relegation zone.
Northampton were plagued by injuries, missing Sam Foley, Dean Bowditch, Ash Taylor and John-Joe O'Toole before kick-off and then losing Shaun McWilliams during the first-half, meaning Pollock was sent on for his debut.
Fellow youth teamers Camron McWilliams and Jack Newell were also on the bench and Jay Williams started again for the third straight game, with Junior Morias also recalled.
Cobblers had to weather an early storm as Cambridge made all of the running with Brown dragging a shot wide and then George Maris clipping the crossbar with a delicious curling effort.
Brown then saw a much better opportunity come his way on seven minutes when he was picked out by David Amoo's cross but, unmarked, he headed wide from just eight yards out.
There was space to play in for both sides in what was an open, stretched start to the game, although all Town had to show for their efforts was a harmless long-range attempt from McWilliams.
But that changed on 27 minutes when, following a more serene passage of play, Northampton struck out of the blue. The ball bounced about in the Cambridge box from a shot corner and eventually fell to Sam Hoskins, whose looping header hit the crossbar and redounded out to Pierre and the centre-back unleashed a superb strike into the top corner.
Town survived a couple of lose shaves as United continued to find oceans of space on the counter-attack, the visitors bailed out thanks to alert goalkeeping from David Cornell and then the indecision of Amoo nor Brown with neither able to turn in an inviting cross.
An injury to McWilliams forced Curle into a change and on came Pollock for his Cobblers debut, but Town couldn't see out the rest of the half without losing their lead. In the third of four added minutes, Rushian Hepburn-Murphy teed up Brown who conjured up a finish to match that of Pierre's, using the outside of his left foot to brilliantly find the far corner.
Northampton started the second-half with teenagers Williams and Pollock in central midfield but that didn't seem to faze them as they quickly reclaimed the advantage. United just couldn't deal with Buchanan's week shot three minutes into the half and the ball dropped perfectly for Morias to lash into the net.
Morias spurned a clear opportunity to score a swift second, just unable to turn in after good work by Bridge, and then it was the home side's turn to miss an even better chance.
Brown both won and took a penalty, tripped by Shay Facey, but despite sending Cornell the wrong way, his effort rebounded off the woodwork and away to safety.
Hepburn-Murphy whipped a free-kick narrowly over and United were soon back on level terms shortly after the hour-mark when Brown's set-piece was headed in by Taft at the back post.
Given Town's patched-up team, it was no surprise that Cambridge were the side pushing for a winner in what time remained as Harrison Dunk got his feet tangled up when presented with a shooting chance before Jabo Ibehre failed to smuggle the ball home from close-range.
Facey also produced a last-ditch sliding challenge on Amoo and Taft headed a corner wide for the home side before Ibehre also missed the target.
Williams blazed over in a rare chance for the Cobblers but there was an element of inevitably about what occurred in injury time.
Cambridge were utterly dominating by this stage and they eventually made it count with virtually the last kick. Town failed to clear their lines and the ball pinged around in the box before dropping kindly to Amoo, who lashed in to send home fans wild and break away fans' heart.
Cobblers: Cornell, Facey, Pierre (c), Turnbull, Hoskins, Cox (Buchanan 45), J Williams, S McWilliams (Pollock 43), Bridge, Morias (Powell 58), A Williams
Subs not used: Coddington, Odoffin, C McWilliams, Newell
Cambridge: Mitov, Halliday, Carroll (Dunk 62), Taft, Taylor, Deegan (c), Amoo, Hepburn-Murphy (Azeez 76), Maris (John 90), Brown, Ibehre
Subs not used: Pilkington, Osadebe, Darling, Lewis, Azeez
Referee: Martin Coy
Cobblers fans: 918