Cobblers relegated to League Two after being dispatched by Blackpool in final home game
Town's fate sealed with one game to spare
Cobblers will make an immediate return to League Two next season after their relegation was confirmed via a crushing 3-0 home defeat to Blackpool on Saturday.
Having only gained promotion back to League One in June, Town's return to the third tier lasted just one season as goals from Luke Garbutt and Jerry Yates sealed their fate once and for all.
Not for the first time in recent weeks, Cobblers competed admirably against promotion-chasing opponents and even had the better of much of the first-half, however another avoidable goal undid their hard work.
Garbutt smashed in from a tight angle and the home side never looked like getting back into the game in the second-half before their woes came to a rather fitting end when conceding two poor goals late on.
Jon Brady and his players have not gone down without a fight but they were simply outclassed by a superior side at the PTS and confirmation of their relegation is in some ways the natural end point of what has been a disappointing, error-strewn campaign.
The club will have plenty of questions to be answered once they sign off their campaign at Sunderland next weekend, not least in the dugout with Brady's time as an interim boss coming to an end.
Brady named an unchanged line-up and his side made a bright start at the PTS as Alex Jones and Mickel Miller threatened down the left before Ryan Watson saw a strong penalty shout turned down.
Town lost Joseph Mills to an ankle injury on 10 minutes, replaced by Michael Harriman, but they were given a big chance to go ahead only a minute later as a defensive slip allowed Jones in on goal, only for the striker to also lose his footing with just goalkeeper Chris Maxwell to beat.
Despite the home side's positive start, though, it was Blackpool who struck against the run of play on 19 minutes and whilst it was a fine strike by Garbutt, Jonathan Mitchell would have been disappointed to concede from such an acute angle.
Cobblers continued to get into good positions and cause issues for the away side, but clear-cut chances were few and far between, and they were indebted to their goalkeeper shortly before half-time when Mitchell atoned for his part in the goal by producing a strong save against Jerry Yates.
Town remained behind at half-time after Miller just failed to reach Jones' through pass in first-half stoppage-time, and Brady went for broke at the break, sending on two strikers in Danny Rose and Ryan Edmondson.
It was an action-packed start to the second-half as Hoskins ballooned over at one end before Blackpool twice went close at the other, Fraser Horsfall producing a vital last-ditch tackle on Ellis Simms and Harriman then in the right place to clear Danny Ballard's header off the line.
Mitchell's services were also required when he was at full stretch to keep out Kenny Dougall's low shot as the visitors went about their business with little cause for alarm.
With Wigan losing elsewhere, Cobblers desperately needed a goal to give themselves a sniff going into the final game of the season but they were unable to create anything of note in attack.
Caleb Chukwuemeka and Mark Marshall were both introduced with 17 minutes to play but within 90 seconds, Blackpool sealed the deal when Mitchell fumbled a shot and Yates was on hand to score the rebound.
Simms was denied by Mitchell late on but Yates wrapped things up with his second and Blackpool's third four minutes from time, compounding Northampton's misery and sending them back to League Two with a bump.
Cobblers: Mitchell, Kioso, Horsfall, Jones, Mills (c) (Harriman 10), McWilliams (Rose 45), Morris, Watson (Chukwuemeka 73), Hoskins, Miller (Marshall 73), Jones (Edmondson 45)
Subs not used: Woods, Bolger
Blackpool: Maxwell (c), Turton, Ballard, Thorniley, Husband (Ekpiteta 79), Garbutt, Dougall, Robson (Gabriel 36), Embleton (Anderson 86), Simms (Holmes 87), Yates (Mitchell 87)
Subs not used: Moore, Shaw
Referee: Peter Wright