We were denied an incredible victory by a last-gasp equaliser on an unforgettable day at Blundell Park.
In the second of seven added minutes at the end of the match, David McGoldrick put us ahead for the first time as it looked like we had secured the three points.
But, moments after the restart, Mariners substitute Harry Wood curled an effort into the top corner to earn his side a draw.
We'd found ourselves 2-0 down after 15 minutes, Danny Rose (pen) and Abo Eisa punishing our slow start.
But we went into the break level as McGoldrick then Macaulay Langstaff converted Jodi Jones crosses.
Harry Clifton put his side back in front early in the second half, only for Aaron Nemane to convert another Jones cross to level things up at 3-3.
Two minutes later we were behind again as Eisa produced a clinical finish - but deja vu soon struck as Jones laid on another cross for Nemane to score his second, setting up the dramatic finish in stoppage time.
In what was the first match after Luke Williams’ departure for Swansea City, the interim management team of Jim O’Brien, Tom Weal and Joao Alves had the responsibility of selecting the team.
In goal, Aidan Stone was favoured to Luca Ashby-Hammond following the latter's recent loan arrival from Fulham.
Ahead of them, Connell Rawlinson came into a back three alongside Aden Baldwin and Kyle Cameron, while Scott Robertson was handed his debut next to John Bostock in central midfield following his arrival from Fleetwood Town.
Jones and Nemane continued out wide, with the familiar attacking trio of Dan Crowley, McGoldrick and Langstaff keeping their places.
O’Brien was on the bench alongside Ashby-Hammond, Richard Brindley, Lucien Mahovo, Tobi Adebayo, Sam Austin and James Sanderson.
The travelling fans packed into the sold-out away end will have been hoping for a bright start but, after Stone had been forced into an early low save from Eisa, the winger caused havoc once again and drew a penalty from Bostock who was adjudged to have pulled him back in the area.
Rose blasted the spotkick beyond Stone, who soon had to make another save low down to his left as our rocky start continued.
And, soon after Langstaff had sent an effort wide with our first threatening moment of the match on 10 minutes, we were 2-0 behind as the ball dropped for Eisa from a corner and he was able to lash it home.
The pace of the game slowed a little after that but Grimsby would come close to a third on 28 minutes as the referee waved away Robertson’s appeals for a foul, allowing a Grimsby player to square the ball for Clifton to guide an effort on to the bar from inside the area.
A minute later there was a chance for Langstaff, whose attempted left-footed lob was held by Harvey Cartwright. That sparked a break which resulted in Stone making another good save down to his left.
The dangerous Eisa dipped a 30-yard effort narrowly over as the hosts continued to threaten to extend their lead – but we managed to get more of a foothold in the game as the half wore on and had a goal back on 39 minutes when Jones pounced on a loose ball and saw his excellent low cross just evade Langstaff before being turned home by McGoldrick on the slide.
And six minutes later we were level in almost identical fashion, Crowley finding Jones brilliantly and Langstaff this time meeting his cross to turn the ball home from six yards.
The challenge now was to kick on in the second half but we fell behind once again on 52 minutes as Clifton burst into the area and fired a low effort across Stone and into the far corner.
Our first change saw Robertson make way for Austin and the substitute led our charge for an equaliser, making a bursting forward run which was met by a pinpoint long ball from Stone. The midfielder couldn’t quite bring it under his spell to fire goalwards.
But, after Cartwright had kept out a McGoldrick header and Baldwin had seen a long-range effort whistle narrowly wide, we were level once more as Jones yet again found the perfect cross, this time for Nemane to chest the ball home inside the six-yard box.
Two minutes later, however, we found ourselves behind yet again as a ball into the right-hand channel allowed the hosts to fire a dangerous low cross into the middle. Rawlinson stretched to deal with it but the loose ball ran for Eisa to lash home his second of the day.
With the score now at 4-3, we had half an hour to haul ourselves back into the contest and, shortly after Nemane had fired an effort over while surrounded by defenders, Cartwright let a Jones shot slip through his grasp and on to the crossbar. The rebound just evaded Langstaff and Nemane’s stooping header was agonisingly cleared off the line.
Nemane wasn’t to be denied his second for much longer, though, as on 79 minutes he levelled the scores for the second time – and once again it came from a Jones cross, this time a searching one from deep which bounced across the face of goal and was finished well from a tight angle.
Seven minutes were added on at the end of the blockbuster and, in the second of those, we thought we’d won it when Austin zipped the loose ball from Crowley’s half-cleared cross to McGoldrick and watched on as the forward brilliantly worked the finish into the far corner.
But our celebrations were short-lived as moments after the restart Town debutant Wood picked out Stone’s top corner from 20 yards to earn his side a point in what would transpire to be the first 5-5 draw in our history.
STARTING XI: Stone; Cameron, Baldwin, Rawlinson (Brindley 74'); Jones, Nemane (Adebayo 90+3'); Robertson (Austin 56'), Bostock; Crowley, McGoldrick, Langstaff
SUBS: Ashby-Hammond, Mahovo, O'Brien, Sanderson
BOOKINGS: Baldwin 23', Robertson 45', Jones 84'
ATTENDANCE: 7,567 (1,188)