The Mariners beat Sheffield Wednesday at Hillsborough to reach the last 16 of the Carabao Cup for the first time since 2001.
Jaze Kabia’s second-half header proved enough for Town to overcome the Sky Bet Championship Owls and secure their place in the draw for round four.
After their victory over Manchester United at Blundell Park in the previous round, David Artell’s side faced higher-division opposition once again and they were backed by more than 5,000 travelling supporters in South Yorkshire.
And after having the better of a goalless first half against a youthful Wednesday side, the visitors made their pressure count when Kabia struck four minutes after the break.
The home side pushed forward as the clock ticked down but they could not find a way through the resilient Town defence and it was the Grimsby supporters who were celebrating at the final whistle.
Reece Staunton and Justin Amaluzor came in for Jayden Sweeney and Darragh Burns as Mariners head coach Artell made two changes to the team that started Saturday’s 1-1 League Two draw with Cambridge United.
Christy Pym started in goal, with Harvey Rodgers, Tyrell Warren, Cameron McJannet and Staunton forming the defence. George McEachran sat behind Amaluzor, Kieran Green, Evan Khouri and Charles Vernam in midfield, with Kabia selected as the striker.
Sweeney and Burns were both named on a nine-man substitutes’ bench, along with Charlie Casper, Jamie Walker, Jude Soonsup-Bell, Neo Eccleston, Geza Turi, Henry Brown and Clarke Oduor.
Wednesday reached this stage of the competition with a superb penalty shootout victory of their own over Premier League Leeds United and as he did for that game, manager Henrik Pedersen again selected a young starting XI featuring several members of the club’s academy squads.
Goalkeeper Ethan Horvath was the only player to remain in the line-up following the Owls’ 3-0 home defeat by Bristol City in the Championship last time out, although first-team striker Jamal Lowe would look to cause a major threat and club captain Barry Bannan was among the more experienced names kept in reserve on the bench.
FIRST HALF
Horvath claimed a cross from Vernam on the left after an early Town free kick, before Kabia was caught offside to end another move in a bright opening to the game from the away side.
A foul by McEachran gave the hosts an opportunity to attack from a free kick on 12 minutes and Jarvis Thornton’s ball into the box from it looked dangerous but Cole McGhee could only turn it wide of the far post.
A free kick followed at the other end when Vernam was tripped just outside the penalty area. The winger took it himself but Horvath pushed his shot clear.
Kabia was just wide with a snap-shot from 18 yards soon afterwards, before McGhee saw the first yellow card of the night for a shirt-pull on Amaluzor but Town were unable to profit from the free kick.
Rodgers hit the side-netting with a cross from the right on 20 minutes as the Mariners continued to dominate, although only a superb challenge from Warren stopped home striker George Brown from opening the scoring on 26 minutes as he looked to convert a low cross from six yards after a quick break.
Wednesday were forced into making two substitutions on 36 minutes after Reece Johnson and Olaf Kobacki both went down with injuries during the same passage of play. Gabriel Otegbayo and Yisa Alao replaced them.
Staunton saw the yellow card for a trip on Sean Fusire in the centre-circle, then McJannet had to turn a low cross behind for a corner a minute before the break. McEachran headed the flag-kick clear at the near post.
Rodgers did well to win a goal kick at the end of another home attack as the half moved into at least four added minutes, before Green won a corner at the other end. Staunton’s delivery was headed wide at the far post by Warren.
No further chances came before the half-time whistle, so it remained goalless at the interval.
SECOND HALF
Neither side made further changes before the restart and an early Green cross was cut out, before McEachran won a free kick in a dangerous, central position. Vernam shot from it but Horvath tipped his 25-yard strike over the bar for a corner.
From the flag-kick, the Mariners broke the deadlock, as KABIA’S near-post header deflected off McJannet and landed in the net.
Amaluzor missed the target from 20 yards as Town looked for a quickfire second goal, before Walker replaced Green in the visitors’ first substitution on 53 minutes.
Amaluzor had the ball in the net as he tapped in a low cross soon afterwards, although the offside flag had already gone up against Vernam before he sent it across the six-yard line from the left.
Alao brought Amaluzor down to give Town another free kick in a promising position three minutes before the hour but this time, Kabia’s header looped through to Horvath.
Good hold-up play by Kabia got the Mariners back on the front foot after Brown had created an opening for the hosts, then Walker won a corner on the left but it was cleared as far as Khouri, who volleyed through to the keeper from distance.
Walker fired wide from 20 yards as the visitors continued to attack in search of a second goal, before McGhee headed harmlessly over the bar from a Rio Shipston free kick at the other end.
Vernam sent a curling strike over the bar from the edge of the box, then Bannan and Ike Ugbo replaced Fusire and Brown as the hosts looked to their bench in a bid to get back into the contest.
Burns and Oduor came on for Vernam and Kabia with 12 minutes remaining, then Otegbayo became the latest to be booked after pulling Walker down on the halfway line.
Eccleston replaced Khouri on 87 minutes, with Charlie McNeill coming on in the blue and white of the hosts at the same time.
McEachran headed a Bannan corner clear soon afterwards, before Pym comfortably claimed a cross from the home left.
Warren made a good block from Ugbo as Wednesday kept coming forward in search of an equaliser.
They were given a minimum of five added minutes to find a way of taking the game to penalties but Town continued to hold firm at the back, with Warren making another fine block to deny Ugbo.
And despite their late pressure, Wednesday could not find a way through as the Mariners saw out the remainder of the game to secure their place in the draw on Wednesday, September 24 for the next round of the competition..
Attention now switches back to the league programme, with Town set to travel to Barnet on Saturday.
Town: Pym, Rodgers, Warren, McJannet, Staunton, McEachran, Amaluzor, Green (Walker, 53), Khouri (Eccleston, 87), Vernam (Burns,, 78), Kabia (Oduor, 78)
Subs not used: Casper, Sweeney, Soonsup-Bell, Turi, Brown
UTM