Richie Smallwood's stoppage-time penalty rescued a late point for the Bantams, who battled to a 1-1 Easter Monday draw at Blundell Park.
In what was a cagey affair, neither team proved able to stamp their authority on the match in the first 45, with a header from Tyler Smith being the best opportunity of the bunch.
A deflected effort from Curtis Thompson gave the hosts the lead shortly after the restart, but a 93rd-minute spot kick converted by the Bantams' skipper saw the spoils shared.
Grimsby started the stronger of the two teams, enjoying the bulk of the possession in the opening 15 minutes, but with no real chances created, as the game was often broken up with the regular awarding of free-kicks.
After a strong start by the hosts, they were forced into an early change as goalkeeper Harvey Cartwright was forced off with injury, allowing City to regain a foothold.
Tyler Smith had the first effort on target of the game, which did not come until the 33rd minute for the Bantams. Calum Kavanagh won the ball back high up the field, but Smith’s header was straight at Jake Eastwood in the Grimsby net.
The Mariners had their best chance of the half right as it was about to end. Harvey Rodgers latched onto a good ball in but could not direct his header goalwards.
City started the second half on the front foot, with Bobby Pointon curling an effort narrowly over as the half began.
It would be the hosts however who would take the lead in the 55th minute through Curtis Thompson. A corner was only cleared as far as the home midfielder, and his powerful effort took a wicked deflection past Sam Walker.
City were trying to push back into the game, however were struggling to gather much momentum as the tie ticked into its closing stages.
Kavanagh, Smith and Walker all went close, before the Bantams were awarded a golden opportunity to equalise from the penalty spot in stoppage time, as Brad Halliday was dragged to the floor and Denver Hume was shown a red card.
Captain Richie Smallwood stepped up and smashed the spot-kick home to net his first goal of the season and rescue a point for Graham Alexander's side.
GRIMSBY: Harvey Cartwright (Jake Eastwood 17’), Liam Smith, Harvey Rodgers, Curtis Thompson, Gavan Holohan, Jamie Andrews, Justin Obikwu (Donovan Wilson 69’), Douglas Tharme, Toby Mularkey, Danny Rose (C), Denver Hume. SUBS NOT USED: Abo Eisa, Charles Vernam, Callum Ainley, Harry Wood, Evan Khouri.
GOALS: Thompson (55’).
CITY: Sam Walker, Brad Halliday, Matty Platt, Richie Smallwood (C), Calum Kavanagh, Tyler Smith (Harry Chapman 77’), Ciarán Kelly, Daniel Oyegoke, Bobby Pointon (Jamie Walker 64’), Jonathan Tomkinson (Clarke Oduor 64’), Lewis Richards (Tyriek Wright 77’). SUBS NOT USED: Colin Doyle, Liam Ridehalgh, Noah Wadsworth.
GOALS: Smallwood (90+3’ pen).
ATTENDANCE: 6,711 (with 788 travelling City supporters).
