Grimsby were in trouble early on having defended a constant Wrexham onslaught the home side took the lead just before half time when a long clearance upfield was headed down by John Walters for Mark Jones to unleash a long distance shot that gave the Mariners keepers no chance.
Grimsby were in deeper trouble straight after time when centre half Rob Jones was replaced by Martin Gritton, then the other centre back Simon Ramsden was injured in a clash with Wrexham's Dave Bayliss and had to go off.
It caused a reshuffle and Wrexham might have taken advantage within two minutes Grimsby were level. Gary Cohen made the opening with a superb cross field ball that Michael Reddy hit home for his eight goal of the season waiting for the keeper to go down before chipping over him.
Wrexham's Mark Jones hit the post and Walters saw a sot deflected wide but Grimsby began to grow in confidence as the game went on.
Cohen was unlucky not to get the touch when a cross from Reddy went inches in front of him in the box.
With the game hotting up with the substitute Glen Downie burst through to head the winner from Tom Newey's free kick two minutes later Grimsby fans were confused to see referee Deadman produce a red card for Paul Bolland and who was equally bewildered.
After a check with fourth official the referee realised he had mistaken the Grimsby number eight for Wrexham Danny Williams who had been booked earlier and changed his mind showing, Bolland only a yellow and let him stay on.
In time added on Wrexham's Williams did get a red card and sent off from retaliation.