Morecambe moved 10 points clear of the drop zone after this draw at the Globe Arena.
The Shrimps were heading for a fourth successive home win after Aaron Collins put them ahead from the penalty sport 10 minutes from time but the visitors hit back with their first goal in five games when Charles Vernam slotted home a right wing cross with just two minutes remaining.
Boss Jim Bentley made one change to the starting line up from the 1-1 draw at Macclesfield Town a week earlier with Richie Bennett replacing Collins up front.
Morecambe certainly started sharply with Liam Mandeville driving straight at the Grimsby defence from the kick off and shooting wide from 30 yards with just four seconds gone.
Moments later and the same player had a shot blocked after Grimsby keeper James McKeown punched Piero Mingoia’s cross away from goal.
Kevin Ellison the blazed a volley over the bar as the Shrimps started well.
After a sluggish start the visitors began to create chances of their own with Barry Roche making a good save low to his right to keep out Vernam’s header.
The Shrimps’ keeper then saved Joe Grayson’s long-range shot with his legs before Martyn Woolford’s shot was deflected just wide of goal by one of his team-mates.
Roche continued to be the busier of the keepers with a scrambling save from Danny Collins’ header before pushing out Vernam’s effort moments later.
Grimsby then had a golden chance to open the scoring on 35 minutes when the ball fell to Grayson on the edge of the box but the young Blackburn loanee made a real hash of his final effort which he fired well over the bar.
The Shrimps came back with Aaron Wildig curling a shot just wide of the target after a neat turn in the box and Mandeville had another blocked just before the break.
The second half saw much less goalmouth action with both sides failing to make the final ball tell until a frantic final 10 minutes after the Shrimps took the lead in the 80th minute.
Andy Fleming’s long ball forward saw Collins beat the last man for pace before progressing into the area.
He tried to round McKeown, only to be brought down by the keeper, but then sent him the wrong way from the spot.
However, with time running out, the visitors drew level when Kristian Dennis controlled Harry Davis’s cross a ball and his lay off was converted by Vernam to deny the Shrimps a fourth successive home win.
Morecambe: Roche, Mills, Lavelle, Old, Conlan, Mingoia (Cranston 79), Fleming, Wildig, Ellison (Collins 67), Mandeville, Bennett (Oliver 63). Subs not used: Halstead, Kenyon, Sutton, Brownsword.
Grimsby Town: McKeown, Hendrie, Davis, Collins, Ring (Whitmore 83), Vernam, Hessenthaler, Woolford (Hall-Johnson 83), Grayson, Cardwell (Clifton 76), Dennis. Subs not used: Russell, Buckley, Burrell, Pollock.
Referee: Scott Oldham.