The result was rough justice for Brian Carey and his team, who took the lead with their first goal in seven-and-a-half hours only to be pegged back in first half added time from a corner.
And clearly the Welsh side had not learnt their lesson for they were undone in the final minute of an enthralling game as Grimsby snatched the three points for a fourth successive victory.
Grimsby playing the favoured 4-5-1 system could not get going early on and it was a lively Wrexham who started much the better side. Mark Jones and Mike Carvill had good chances before Wrexham broke their goal drought on 28 minutes with a bizarre effort.
Midfielder Ciaran Toner, for some reason best known to himself, played the ball back towards his own goal which Wrexham striker Lee McEvilly latched onto it. And, although keeper Phil Barnes saved his first shot and then his second effort came back from the post, the striker finally scrambled the ball in to make it third time lucky.
Grimsby's system was just not working as striker Martin Paterson was all alone up front with no support.
Manager Alan Buckley decided enough was enough and sent on striker Gary Jones to lend some support to the Stoke striker, who was playing his last match on loan for Grimsby.
And just when Wrexham looked as if they would reach half time in front, they conceded their first corner of the half in added time and Danny Boshell's well taken kick was met superbly by the head of midfielder Paul Bolland and the ball arched up in the air and dropped in under the angle.
It was cruel on Wrexham who had dominated the half, but Grimsby came out for the second half like men possessed and they were struggling to hang on to the 1-1 score line.
Paterson, who was determined to end his loan spell with a goal, curled a beautiful low shot inches past the far post.
As the fascinating game drifted to its close it was Wrexham who looked the stronger. But with virtually the last kick of the game a loose clearance was nodded down and Toner smashed the ball into the net for Grimsby's winner.