Goals at the end of normal time and extra time consigned us to defeat in the Vanarama National League play-off elminators.
We had taken the lead in the second half of normal time through a Ruben Rodrigues penalty, only for the visitors to scramble home a goal from a free-kick in the sixth of six added minutes.
And it was the same story in extra time as the ball was bundled home from another free-kick in the dying embers, leaving Grimsby to progress to the semi-finals.
Ian Burchnall made one change to the starting XI that beat Maidenhead on the final day of the regular season as Adam Chicksen, who was rested as a precaution at York Road, came in at left wing back in place of the bench-bound Dion Kelly-Evans.
Jayden Richardson was deployed on the opposite flank with a back three of Kyle Cameron, Alex Lacey and Richard Brindley protecting Sam Slocombe, who was making his 100th appearance between our sticks.
Matt Palmer, Jim O'Brien and Cal Roberts were our midfield trio, with Rodrigues partnering Kyle Wootton up front.
The visitors edged the opening exchanges and came close to an opening goal on 13 minutes when Erico Sousa's header flashed wide of the post.
We were then dealt a major blow when, on 22 minutes, Roberts was forced off with an injury. Elisha Sam replaced him, with Rodrigues dropping into midfield.
Sam registered our first shot on goal shortly afterwards, his tame effort being comfortably saved by Max Crocombe, but we came much closer on 31 minutes when Richardson did brilliantly to cross for Rodrigues only to see the Portuguese send his diving header over the bar.
A cagey first half ended with bookings for O'Brien and Harry Clifton for lunging challenges, the former's appearing harsh as he looked to cleanly win the ball from Sousa.
There were no changes at the break and the Mariners had the better of the early second-half exchanges, Clifton and Holohan flashing efforts narrowly wide and Brindley making an important block before O'Brien made way for Ed Francis.
And the substitute, along with Chicksen, had to get in the way of another Grimsby effort shortly after his introduction as the visitors continued to have the better of things.
The tide began to turn though and, after Sam's cross had been too far behind Wootton for the number nine to make clean contact with his header, we were given a magnificent chance to take the lead when Rodrigues' goalbound shot was handled in the area by Andy Smith.
Rodrigues had to wait patiently to take the spotkick but, in front of a packed Kop, he kept his cool to slot the ball home and give us a precious advantage.
We came close to securing our spot in the semi-finals twice in quick succession shortly afterwards with Rodrigues seeing a left-footed shot saved moments before Wootton's header was diverted just wide.
It nevertheless looked like one goal would be enough as the lion's share of six minutes' added time passed with our defence standing up to Grimsby's desperate attempts for an equaliser.
But, at the death, we concded a cheap free-kick on the edge of our own box which presented Town with the chance to throw everyone forward, including keeper Crocombe, and the result was Gavan Holohan bundling the ball home with the last kick of the game.
Despite the crushing disappointment we began extra time on the front foot with Sam almost capitalising on a misplaced defensive header before Cameron's goalbound effort was hacked away by a defender.
The Grimsby rearguard were called into action again minutes later when Sam burst into the box only for a Town man to make a big block from his shot.
Wootton whizzed an effort over the angle of post and crossbar before Grimsby claimed their only shot of the half as Slocombe pushed Sousa's strike away.
We continued to look the more likely side to score as Brunt saw another effort blocked before his follow-up was saved.
Shortly afterwards, Wootton got the run on his defender as they chased a ball into the box but the forward couldn't get a meaningful shot away.
Despite our best efforts it looked like penalties were looming large, although we were given a minor scare when Slocombe had to get down to push Abrahams' shot away.
But it was a case of deja vu in the final minute as another free-kick led to substitute Emmanuel Dieseruvwe scrambling the ball home despite appearing to be in an offside position.
We were given three added minutes to rescue our play-off campaign, during which Sam controlled the ball in the area but fired it over on the turn.
And that proved to be our final opportunity as our 2021-22 campaign ended in heartbreak.
STARTING XI: Slocombe; Cameron, Lacey, Brindley; Chicksen, Richardson (Kelly-Evans 113'); Palmer, O'Brien (Francis 60'), Roberts (Sam 22'); Rodrigues (Brunt 82'), Wootton
BOOKINGS: O'Brien 38', Brunt 110'
ATTENDANCE: 12,023 (2,013)