Danny Rose struck in the seventh minute of stoppage time to earn the Mariners a point from a 1-1 draw with Gillingham at Blundell Park.
Town started the game brightly, with Charles Vernam catching the eye on his return to the starting line-up.
But the visitors took the lead against the run of play through an own-goal scored by the unlucky Doug Tharme.
The hosts came under pressure after the break as Gillingham aimed to add to their lead but they were unable to find a second goal and Rose scored with seconds to spare to claim a share of the spoils.
Four changes were made to the Grimsby team after Saturday’s defeat at Barrow, with Doug Tharme, Curtis Thompson, Vernam and Rose coming in for Cameron McJannet, Denver Hume, Jayden Luker and Justin Obikwu.
Jordan Wright began in goal and was protected by a defence of Lewis Cass, Harvey Rogers, Tharme and Evan Khouri. George McEachran and Kieran Green joined Thompson in the centre of midfield, while Vernam and Jason Svanthorsson lined up either side of striker Rose.
McJannet, Obikwu and Luker were all named on the bench, alongside Seb Auton, Matty Carson, Callum Ainley and Tyrell Warren.
Gillingham made the journey north from Kent aiming for three points to help improve on a league position of 17th at kick-off.
Recently-appointed manager John Coleman would look to the likes of Crystal Palace loanee Asher Agbinone to cause problems for the Town defence.
FIRST HALF
Vernam saw a low strike blocked in the opening minute, then Green lifted a shot on the turn over the bar after a free kick broke for him inside the six-yard box as the Mariners made a fast start.
Wright claimed a cross from Remeao Hutton as the away side attacked for the first time on eight minutes, before Agbinone burst into the penalty area on a pacy run from the left. His low cross was half-cleared after it had been helped on towards goal and the ball broke for Armani Little to fire over the bar from 25 yards.
A foul by Hutton on Svanthorsson gave Town a free kick on the left, although Vernam’s delivery to the far post was headed away.
Agbinone was off-target on 17 minutes after taking advantage of a mistake in the home defence, before a long throw from Hutton found Agbinone but he could only turn the ball through to Wright.
Town were still looking bright in possession and another opportunity came when Vernam picked Green out with a cross from the right, although the midfielder could not direct his header towards goal.
A foul on Svanthorsson then brought a free kick in a dangerous, central position and Vernam’s strike got a slight deflection which took it narrowly wide for a corner. Vernam and McEachran worked a short corner routine but the winger’s cross was headed away.
Tharme sent a long throw into the box soon afterwards and it looked to have caused problems until the offside flag went up.
A stoppage came for McEachran to receive treatment after feeling the effects of a strong challenge, then when the game restarted, Town created the next chance as another Vernam cross found Green, who headed wide.
A pull-back from Green proved to be just behind Svanthorsson as the hosts kept pushing forward.
But when the opening goal arrived on 35 minutes, it was Gillingham who took the lead, as a cross from Jack Nolan on the right was sliced into his own net by the unfortunate Tharme.
After the goal, the visitors increased the tempo but Town’s response was positive, with Svanthorsson cutting inside from the left and hitting a low, 20-yard effort which away keeper Glenn Morris got down to stop.
Three added minutes were played at the end of the first half and with no further chances created by either side, the visitors went in at the break with the advantage.
SECOND HALF
No changes were made before the restart and Gillingham were inches away from having a second own-goal in their favour less than two minutes in. Shadrach Ogie crossed from the left and as Green attempted to clear, his diving header bounced off his own bar before being cleared for a corner.
The visitors were making a purposeful start to the half as they attacked in search of a second goal, with Town forced to defend.
Wright did well to race out of his penalty area and clear the danger as Joe Gbode aimed to get to a ball down the away left, then the first yellow card of the night went to Gillingham’s Nelson Khumbeni for catching Cass in a clash in the air.
Gbode followed his team-mate into the referee’s notebook for a push, before Khumbeni made way for Tim Dieng as the visitors made the first substitution.
Town were yet to create a clear opportunity in the second half as the clock ticked past the hour mark and their first change saw Luker replace Vernam on 65 minutes.
Wright kept a header from Dieng out after Ogie had got to a loose ball first and Agbinone chipped a cross to the substitute at the far post.
Tharme headed clear from a Nolan free kick and as Town broke through Khouri, Little earned a booking for bringing him down near the halfway line.
Gbode called Wright into action again soon afterwards with a strike from he edge of the box, which the keeper pushed away. Tharme completed the clearance.
Dieng headed over the bar from a left-wing corner as Gillingham continued to ask the questions in attack.
Town needed a goal and with 12 minutes remaining, they looked to an extra striker as Obikwu replaced Thompson.
The visitors made a double-substitution moments later, with Bradley Dack replacing Agbinone and Oliver Hawkins coming on for Nolan.
Luker cleared the crossbar with a cross from the right just before the game moved into at least seven added minutes.
Town pushed forward and they went close to an equaliser when Luker found Svanthorsson inside the box, although he was denied by keeper Morris, who made a superb save to get the ball away for a corner.
The home pressure continued and a Green volley from Thrme’s long throw was deflected through to Morris in goal.
But the pressure eventually told and the Mariners snatched a point with seconds remaining. Green got down the right and pulled the ball back to the near post, where ROSE was on the spot to send a smart finish past Morris and make it 1-1.
Town had an opportunity to complete an unlikely turnaround when Obikwu burst into the box, although this time, there was a slip as the ball was pulled back and the Gillingham defence recovered.
That proved to be the final chance of the evening, as Town ensured they came away from the game with a point.
The Mariners are next in action on Saturday, when they travel to Bromley.
Town: Wright, Cass, Rodgers, Tharme, Khouri, McEachran (Carson, 90+3), Thompson (Obikwu, 78), Green, Vernam (Luker, 65), Rose, Svanthorsson
Subs not used: Auton, Ainley, McJannet, Warren
Attendance, brought to you by Kingsway Hotel, Cleethorpes: 4,239