Cobblers suffered another day of misery at the hands of rivals Peterborough United when two first-half goals sent them spiralling to a 2-0 defeat at the ABAX Stadium on Easter Monday, inching them closer to relegation from Sky Bet League One this season.
Despite what the half-time scoreline suggested, Northampton bossed the opening exchanges and should have been in front but schoolboy defending and missed chances proved costly when three minutes of madness allowed Jack Baldwin and Jack Marriott to put Posh in control.
It was always going to be difficult to claw the game back from there for a team low on confidence and struggling, and so it proved as the Cobblers barely produced an attack of note in the second-half before having Ash Taylor sent off for a professional foul late on.
Their winlesss run now stands at nine games and with just five matches remaining this season, signs of Northampton getting out of trouble are few and far between.
It was all change for the Cobblers at the ABAX Stadium, both in terms of personnel and system, as Hasselbaink made four alterations from Good Friday's defeat to Charlton and also switched to 4-3-3,
Kevin van Veen, David Buchanan, Brendan Moloney and Shaun McWilliams all dropped to to the bench and in came Sam Hoskins, Daniel Powell, Sam Foley and Leon Barnett, who was making his first start since December 9.
The away fans were in fine voice before kick-off and they were rewarded by a surprisingly positive start by their side, who could easily have been two goals to the good inside 10 minutes.
Posh had barely got going when Conor O'Malley plucked Matt Crooks' goalbound header out of the air, and the young home 'keeper was then at his best to deny Long who had been released through on goal by Crooks' threaded pass.
Town's start offered plenty of encouragement but a crazy two minutes had their fans fearing the worst again.
Having began with such purpose, the visitors switched off in defence and were suitably punished when two hopeful, long free-kicks both, inexplicably, ended in goals.
Totally against the run of play, home skipper Baldwin struck first, heading in Liam Shephard's high delivery on 12 minutes, and then Marriott notched his 31st goal of the campaign just 90 seconds later, neatly lifting over Richard O'Donnell after more criminal defending from a set-piece.
The 2-0 scoreline almost beggared belief given the pattern of the first 15 minutes but having somehow found themselves in control, Peterborough weren't about to ease off and they almost had a third on the break through Chris Forrester, who was denied by Foley's block, and then Gwion Edwards, whose 20-yard curler was saved by O'Donnell.
The two goals had taken the sting out of Town's play, understandably, and while they still carried a threat, Peterborough fancied their chances every time they attacked with only a fabulous sliding challenge by Barnett preventing Marriott from tapping in a certain third
Crooks appeared the most likely man to make something happen for Town and he perhaps should have halved the deficit when pouncing on a defensive mistake, however he took too long and the block came in before the half ended with O'Donnell saving from the menacing Marriott.
The second-half opened with Marriott going close again, only denied his second by the offside flag, as Peterborough looked to extend their advantage.
Northampton were struggling to make much headway and created only one chance throughout the second period, though it was a glaring one when it came along as substitute van Veen latched onto Shay Facey's pass and fizzed in a low cross that was met by a sliding Foley at the back post, but the ball cannoned back off the woodwork.
From then on, the game rather petered out with little or no goalmouth action at either end, however there was to be another dose of misery for the Cobblers 11 minutes from time when Taylor was harshly adjudged to have brought down Marriott with the United striker through on goal, resulting in a straight red card.
The reshuffle saw Facey move to centre-back and Hoskins right-back but Taylor's red was the final nail in the Northampton coffin and their ninth successive game without victory was confirmed by the sound of the referee's whistle after five uneventful minutes of stoppage-time.
Peterborough: O'Malley, Shephard, Hughes, Baldwin (c), Taylor, Edwards (Cooper 74), Forrester (Doughty 90), Ward, Da Silva Lopes, Maddison (Morias 89), Marriott
Subs not used: Bond, Lloyd, Freestone, Grant
Cobblers: O'Donnell, Facey, Taylor, Barnett, Turnbull, Hoskins , Grimes, Crooks (Bunney 87), Foley (Ariyibi 73), Powell (van Veen 57), Long
Subs not used: Cornell, Moloney, Buchanan, McWilliams
Referee: Michael Salisbury
Cobblers fans: 1,435