Stuttering Cobblers suffered a torrid derby day beating as they slumped to a fourth defeat in five games when soundly defeated 3-0 by rivals Peterborough United on a disastrous evening at the ABAX Stadium.
Not for the first time this season, Northampton were undone by a combination of inept defending, poor decision-making and a lack of quality in the final third, with strikers Marc Richards and Alex Revell barely feeding off scraps throughout the evening.
But it was the former, particularly at set-pieces, that was Town's biggest downfall on this occasion with two headers from two corners handing Peterborough a 2-0 half-time lead.
The visitors did at least apply more pressure in the second-half but that owed more to Peterborough being happy so sit back, let their opponents have the ball and then look to break.
And it was on the counter-attack where they scored the killer third goal, completing a wretched evening for Rob Page who now has plenty of thinking to do as he attempts to arrest his side's current slump.
Prior to Saturday, there were thoughts of looking at the play-offs and above but back-to-back defeats to Millwall and now Peterborough, conceding six goals in the process, leave Town 12th in Sky Bet League One, just three points above the drop zone in a tightly-congested table.
That said, they are only three points adrift of the play-offs and with a trip to rock bottom Shrewsbury to come this Saturday, there is an opportunity for Cobblers to get back on track and right some of the wrongs sustained on Tuesday evening.
Page's team selection prior to kick-off raised a few eyebrows as the Cobblers boss made four changes from Saturday with John-Joe O'Toole, Harry Beautyman and JJ Hooper dropped from the side and Jak McCourt suspended.
In came Richards, Joel Byrom, Sam Hoskins and former Posh man Gabriel Zakuani as Page stuck his neck out by starting David Buchanan and Brendan Moloney as wing-backs in a 3-5-2.
A cauldron of noise greeted the two teams as they emerged from the tunnel and it was the typical lively start you expect from a derby with both sets of fans in good voice.
There was no doubt as to which team made the better start, though, with Marcus Maddison first to get a shot away when his low drive was parried away by Adam Smith and that set the tone for the first-half as Peterborough dominated.
Cobblers struggled to get out of their own half at times and the visitors were soon behind when poor marking from a corner allowed Shaquile Coulthirst to head Posh into a deserved 14th minute lead
Hoskins led a spirited if brief Northampton response with a weaving run down the right that culminated in a corner from which Zander Diamond had a close-range shot blocked.
Both sides were finding space when in attack but only Peterborough looked like scoring again and Paul Taylor's 25-yard strike almost doubled their lead as Smith produced a fine flying save.
But Smith's intervention proved futile as straight from Maddison's subsequent corner, a combination of Tafazoulli and Diamond forced the ball over the line from close-range.
Again it was Hoskins who threatened as much as anyone in Northampton colours from the restart as he forced Luke McGee into action for the first time, the Posh keeper handling well in the slippery conditions.
A lack of quality in the final third was again Town's undoing; time and again they worked themselves into promising positions throughout the opening 45 minutes but failed to do anything with it.
As a result, Peterborough went into half-time in the ascendancy and leading 2-0, forcing Page to introduce O'Toole for Byrom for the second-half.
Little changed, however, as Peterborough threatened to run riot with Smith denying Taylor a third immediately after the restart before Moloney pulled off a miraculous goal-line clearance to deny the same man.
Somehow Northampton were holding on and as the second-half progressed, Cobblers threw more men forward with JJ Hooper's introduction signalling a switch to 4-4-2.
A flurry of activity midway through the second period almost yielded a route back into the game for Northampton but first Hoskins and then Moloney saw shots blocked or saved, and that was as close as they came.
As the visitors pushed men forward and Posh threatened on the counter-attack, the game became increasingly stretched and chances arrived at both ends and another goal only seemed inevitable.
That proved the case, and unfortunately for Northampton, it went the way of Peterborough who completed a resounding victory with an excellent third on the break as Gwion Edwards crossed for fellow substitute Tom Nichols to poke past Smith.
That ended a thoroughly disappointed night for Cobblers who now must lick their wounds and look to go again ahead of this weekend's trip to Shrewsbury.
Peterborough: McGee, Smith, Hughes, Bostwick, Tafazolli, Baldwin, Forrester, Taylor (Edwards 77), Maddison, Coulthirst (Nichols 45), Lopes (Chettle 86)
Subs not used: Tyler, White, Chettle, Oduwa, Moncur
Cobblers: Smith, Diamond, Nyatanga (Hooper 59), Zakuani, Moloney, Byrom ((O'Toole 45), Anderson, Hoskins, Buchanan, Revell, Richards (c)
Subs not used: Cornell, Phillips, Gorre, Potter, Beautyman
Referee: Neil Swarbrick
Cobblers fans: 2,172