Defender Will Boyle secured a battling point for Cheltenham Town after a closely fought Sky Bet League Two encounter and a wet and windy Blundell Park.
Grimsby – without a league win in ten games - were ahead inside three minutes as an error at the back post from the Robins gifted new home recruit Simeon Jackson a debut goal.
Joe Morrell came closest to a first half response for the visitors as his dipping 25-yarder was tipped around the post by home stopper Ben Killip.
Morrell did orchestrate the equaliser when his pin-point free kick found Boyle who stooped low to nod home from close range as the game ended all square.
Manager Gary Johnson made two changes to the side that drew with Barnet as Joe Rodon came in for his Football League debut and Brian Graham was recalled.
But a disastrous start saw Luke Summerfield swing in an early free kick before the ball was headed back into the path of Jackson to tuck home from six yards out.
The shell-shocked Robins looked to re-group quickly with Harry Pell, Morrell and Kevin Dawson getting on the ball and new boy Roden looking assured at the back.
A stretching Grimes was close to connecting with Morrell's intelligent ball in as the Robins slowly started to enjoy more and more territory and possession as the half wore on.
Morrell showed some fine individual skill to nutmeg his man on the edge of the penalty area and force a fine low save from Killip before Boyle and Graham looked to force home a corner that was cleated off the line.
At the other end, the powerful and direct Jamille Matt looked to extend the home lead with a stinging volley that Flinders kept out.
Cheltenham had penalty appeals waved away after Boyle tussled for a corner, with referee David Webb instead giving the home side a free kick
Graham then headed into the arms of Killip as he met Morrell's cross.
Home full back Dixon then nearly doubled the Grimsby advantage just before the break when he got in down the left and fired a shot across Flinders that he did well to push aside.
Cheltenham were out early for the second half with Johnson clearly demanding more from his team.
And Winchester almost delivered when he fizzed a shot narrowly wide as the Robins looked to show more urgency.
Johnson made a triple change to try and spark a comeback as Adebayo, Odelusi and Sellars were all thrown on for the final half hour.
The visitors continued to prod and probe for a way through but a determined Grimsby were giving little away.
However, the equaliser finally arrived 13 minutes from time when Morrell produced a peach of a free kick to find an unmarked Boyle to nod home.
Hall-Johnson looked to respond for the home side as he whistled a rising shot over the top and Matt wastefully blazed off target from 15 yards out.
But it was the Robins who could have claimed all three points in injury time when a corner was cleared only as far as Sellars, but after taking down the ball his volley whistled wide.
CHELTENHAM TOWN: Flinders (Gk), Grimes, Pell, Dawson, Winchester, Boyle, Eisa (Odelusi 61), Graham (Adebayo 61), Morrell, Rodon, Chatzitheodoridis (Sellars 61). Subs not used: Lovett (Gk), Atangana, Bower, Onariase.
GRIMSBY: Killip (Gk), Mills, Collins (Hall-Johnson 31), Clarke (c), Dixon, Summerfield, Berrett, Wilks (Jaiyesimi 89), Vernam (Dembele 66), Jackson, Matt. Subs not used: Warrington, Woolford, Vernon, Hooper
REFEREE: David Webb
ATTENDANCE: 3,352 (92 from Cheltenham)