Leyton Orient sealed promotion in League Two with a 3-2 win at Oxford, who in-turn were relegated from The Football League.
The match at The Kassam Stadium was key to everything on the last day and in the end it was agony for the home side.
Oxford had gone ahead through Eric Sabin (14), but the lead last just minutes as Craig Easton (17) levelled.
Gary Alexander then fired Orient ahead just after the hour, but this time Oxford were quick to strike back as Chris Willmott headed his side level.
Willmott was then dismissed late on, before Lee Steele (pictured) - against his former club - pounced to seal the victory.
Grimsby had looked set to deny Orient, as they went ahead 15 minutes from time with a penalty from Jean Paul Kamudimba Kalala.
However, fate was against The Mariners as Ryan Gilligan levelled for Northampton in the final seconds, just as Steele was scoring the winner at Oxford.
Oxford's demise meant that six other teams - Stockport, Notts County, Barnet, Torquay, Macclesfield and Bury - breathed a huge sigh of relief.
Third from bottom Stockport finished there after they drew 0-0 with champions Carlisle at Edgeley Park.
Notts County looked in danger at one point, but they and Bury secured their respective status with a 2-2 draw at Meadow Lane.
The Shakers looked well on course for victory thanks to goals from Dwayne Mattis (41) and Tom Youngs (81), but two goals in the last four minutes from Daniel Martin (86) and Julien Baudet (89 pen) gave The Magpies a share of the spoils.
Torquay's miraculous escape was completed at Plainmoor as they drew 0-0 with Boston.
Barnet made sure they were not reliant on other results as they won at already relegated Rushden & Diamonds 2-1.
The North London side sealed victory just after half time with quick-fire goals from Liam Hatch (51) and Nick Bailey (55).
Simeon Jackson (86) added a late consolation for Rushden.
Macclesfield sealed a last minute win at Bristol Rovers. David Morley (7) opened the scoring early on, before Lewis Haldane (12) levelled.
Marcus Richardson restored Town's lead, but Haldane levelled with his second. Richardson then won the game as he grabbed his brace in the last minute.
Lincoln City sealed their play-off spot with a 1-1 draw with Rochdale at Sincil Bank.
Northern Irish defender Gareth McAuley put Lincoln ahead 18 minutes from time, but Rickie Lambert levelled in the final minute.
Peterborough were the only side who could have stopped Lincoln, but they succumbed 2-0 at home to Wycombe - who themselves were confirmed in sixth place.
The Chairboys grabbed goals in either half through Jermaine Easter (14) and Mike Williamson (85).
Cheltenham Town stopped Wycombe moving fifth, as they romped to a 5-0 win at Mansfield to claim that spot.
Steven Gillespie (34), Ashley Vincent (45), Grant McCann (50), David Bird (pen 81) and Kayode Odejayi (88) helped themselves to goals at Field Mill.
Darlington finished the season with a 1-1 draw against Wrexham at The TFM Arena.
Danny Williams's goal on the half hour looked to have given the Welsh side victory, but Andy Cooke fired home in injury time to grab a point for The Quakers.
Shrewsbury sealed a top-ten finish as they beat Chester 1-0 thanks to Kelvin Langmead's goal after nine minutes.
Click below for match summaries:
Bristol Rovers v Macclesfield
Chester v Shrewsbury
Darlington v Wrexham
Grimsby v Northampton
Lincoln City v Rochdale
Mansfield v Cheltenham
Notts County v Bury
Oxford United v Leyton Orient
Peterborough v Wycombe
R'den & Dmnds v Barnet
Stockport v Carlisle Utd
Torquay v Boston United