Former Cobbler Nicky Adams grabbed two assists as Town were beaten 2-1 by promotion-chasing Bury at Gigg Lane on Easter Monday.
The two teams combined for an impressive 21 shots - Bury having 11 to Northampton's 10 - in a breathless and frantic first-half as Andy Williams' 10th goal of the season was cancelled out by Chris Stokes, set up by Adams, shortly before the break.
But Bury, who started the day in fourth, gave their automatic promotion hopes a major boost with two second-half goals as the outstanding Danny Mayor curled in their second of the day before Nicky Maynard scored with the last kick of the game.
Town could easily have scored more than once having racked up 15 shots and plenty of chances but their inability to make the most of a blistering start, coupled with a late miss from Williams, proved costly as they remain 15th in League Two with two games to go.
Keith Curle promised changes for this game and he was as good as his word when recalling David Buchanan and Shay Facey, alongside top scorer Williams, to the starting line-up.
Scott Pollock started for the third game in a row and the Cobblers made an electric start at Gigg Lane, creating three big chances inside the first five minutes.
Facey headed Buchanan's narrowly over cross with just 90 seconds gone before Buchanan saw a shot saved himself, Daniel Powell off target with the rebound, and then home goalkeeper Joe Murphy stood tall to block from Williams.
Such was their quick start, Cobblers had racked up six shots by the 10th minute although the visitors' willingness to push men forward was in turn leaving space for a dangers Bury team during an open and frantic first quarter.
Having weathered the early storm, Bury settled into the game and started to gain control of possession, though two important blocks from Charlie Goode and another by Aaron Pierre ensured David Cornell remain untroubled in the opening 25 minutes.
Whilst not quite as threatening as earlier in the game, Town continued to pose problems for their hosts and that was illustrated on 28 minutes when they took a surprise lead. Williams was the scorer - heading home his 10th of the campaign - but it all owed to the sterling work of Sam Foley, who won back possession and put it on a plate for the striker to nod beyond Murphy.
Powell and Williams then had shots blocked but though Bury's defence remained unconvincing at one end, their attack was slick and menacing at the other and six minutes before the break they were level.
It was a well-worked equaliser as referee Michael Salisbury played an excellent advantage which allowed Shakers captain Adams to skip away from former team-mate Buchanan and whip in a terrific cross for Stokes, whose well-controlled, first-time finish nestled into the top corner.
That got Bury's tails up again and they finished a thoroughly enjoyable first-half on top before coming out strongly in the second, seeing a strong penalty shout turned down when Maynard took a tumble inside the box.
The second period was a little less helter-skelter than the first but Bury were on top and they came within a whisker of going ahead when the brilliant Mayor, who ran the show for the home side throughout, cut inside and curled just wide of the top corner.
That was only a sighter for the midfielder, though, and next time he would not miss. Midway through the second-half, Mayor turned Foley one way and then the other to create space before picking out the bottom corner from 20 yards
With Bury desperate for the points in their promotion chase, the tension went up a notch at Gigg Lane and home nerves weren't helped when Cobblers pushed for an equaliser in the final 10 minutes.
And the visitors created a clear chance to snatch a point when Dean Bowditch's superb pass released Williams in the penalty box but although his dinked effort beat the onrushing Murphy, it drifted agonisingly wide of the far post.
Five minutes of stoppage-time got nerves jangling again but victory was secured with the final kick of the game when Adams picked out Maynard and he beat Cornell, making for a harsh final scoreline on the Cobblers.
Bury: Murphy, Stokes (Moore 62), Aimson, Thompson, Adams (c), Rossiter, Telford (Lavery 73), Wharton, O'Shea (O'Connell 80), Mayor, Maynard
Subs not used: Moloney, Moore, Cooney, Omotayo, Danns
Cobblers: Cornell, Goode, Pierre (c), Turnbull, Facey (Bridge 74), Buchanan (Morias 86), Foley, Pollock (Bowditch 64), Hoskins, D Powell, A Williams
Subs not used: Coddington, Cox, J Powell, Elsnik
Referee: Michael Salisbury
Cobblers fans: 254