Max Crocombe saved two penalties as the Mariners booked their place in the knockout stages of the Papa John’s Trophy with a shoot-out victory over Manchester City U21 at Blundell Park.
Keke Simmonds rifled a shot into the net from 20 yards to open the scoring against his old club from Town’s first attack of the game, before Will Dickson levelled the scores on 17 minutes.
Home attacks were few and far between for the remainder of the first half as City controlled possession and probed for openings, with Town mostly content to let them have the ball in non-dangerous areas of the pitch.
The hosts were brighter after the break and finished the 90 minutes on top, although both sides missed chances to win the game.
That meant penalties, with an extra point on offer to the winner, would determine the outcome of Northern Group F.
And after Crocombe saved from City captain Shea Charles and Oscar Bobb, it was left to substitute Shaun Pearson to convert the decisive spot-kick, making it four successful penalties out of four for Town and sending them through.
Seven changes were made to the Grimsby starting XI, with only Crocombe, Andy Smith, Anthony Glennon and Otis Khan remaining from the team that started the FA Cup victory over Plymouth Argyle on Saturday.
Nevertheless, it was still a strong Mariners line-up, with keeper Crocombe protected by a defence of Jordan Cropper, Smith, Niall Maher and Danny Amos. Glennon moved into a more advanced role on the left side of midfield, with Khan, Kieran Green and Evan Khouri completing the central quartet as Lewis Richardson and Simmonds led the attack.
The substitutes were Jamie Pardington, Pearson, Luke Waterfall, Gavan Holohan, Harry Clifton, Michee Efete and Brendan Kiernan.
Manchester City’s youngsters made the trip east knowing a win would send them through to the knockout stages as group winners, while the scenario was the same for Town as they looked to go from bottom of the section to top over the course of the 90 minutes.
The visitors included Northern Ireland international Charles, who made his debut for his country in a Nations League tie against Cyprus in the summer.
Highly-rated Dutchman Mikki Van Sas was in goal for City, while England U18 international defender Finley Burns and Portuguese winger Carlos Borges would be others to watch.
Town made a perfect start as they opened the scoring with their first attack of the game on three minutes. It was SIMMONDS who registered his first goal for the club as he burst through the middle and let fly from 20 yards to beat Van Sas with a great strike which found the top corner of the net.
A long throw from Cropper soon afterwards was half-cleared after being flicked on by Smith but the hosts retained possession until Glennon’s low ball from the left failed to find a team-mate.
The away side won the evening’s first corner on seven minutes but the ball from the flag was headed away for a throw-in, then the game settled into long spells of City possession, mainly inside their own half.
But after showing patience, the visitors picked their moment to launch a quick, pacy attack on 17 minutes which got them back on level terms. After some nice link-up play around the edge of the box, the ball was slipped through to Borges on the left and his low cross was turned into the net by DICKSON.
Another cross from Borges was then put behind for a corner by Amos as the away side looked to complete the turnaround but after the ball from the flag was headed on, Smith was there to clear it.
After taking an early lead, the Mariners had struggled to put together sustained spells of possession and another City corner came on 23 minutes, with Khouri heading it clear at the near post.
Dickson fired just over the bar from the edge of the box, before Borges won another corner after cutting inside from the left and seeing his low cross blocked.
Another corner followed moments later, this time on the right, but when the ball was eventually played into the penalty area, it was caught by Crocombe.
Scottish attacker Adedire Mebude won another corner after cutting in from the right on 35 minutes and after Town brought the ball clear through Simmonds, the visitors regained possession and won a free kick midway inside their attacking half. Mebude’s delivery was retrieved by Borges but his cross was headed away by Maher.
An offside decision against Richardson stopped the hosts from building a rare attack, before a misplaced pass gave Town some respite with a throw-in on the left, which led to Khan firing over the bar from the edge of the box.
A flashpoint came three minutes before the break after a foul near the touchline on the Grimsby right, with Khan and Cropper both being shown the yellow card in the aftermath.
A Richardson cross was cleared by defender Jadel Katongo, before a shot from Simmonds was blocked after he had turned inside the box as the half moved into two added minutes. The rebound was sent high over the bar by Khouri.
After being content to sit back and watch the visitors keep possession for much of the game so far, Town were now pressing more and their reward was a corner on the right after Khan’s shot was saved by Van Sas, although they were unable to make it count as the ball was cleared in what was the last action of the half.
No changes were made before the restart and a brief stoppage came when Glennon stayed down after picking up a knock in a challenge, although he was able to continue.
A strike from Mebude was comfortably caught by Crocombe on 51 minutes, before Alex Robertson replaced goalscorer Dickson as the away side made the game’s first substitution.
A foul by Khouri on Charles gave City a free kick midway inside the Town half on 56 minutes but the Town midfielder was in place to block the shot when it came from Robertson.
At the other end, a shot by Green was deflected away for a corner on the right, although Glennon’s delivery from it was caught by Van Sas.
Kiernan came on for Glennon and Clifton replaced Khan in Town’s first changes on the hour, before a big chance for the visitors came when they dealt with a Cropper long throw and launched a break through Borges. He got down the left and squared for Mebude but the attacker’s touch let him down and the ball went through to Crocombe.
A foul on Richardson gave the Mariners a free kick near the halfway line but after Charles was booked for bringing the striker down, the ball into the box was caught by Van Sas after it had been headed on by Smith.
Another chance for the visitors came when Bobb drifted through the middle and slipped the ball through to Borges but the winger’s shot was well blocked by Crocombe before a number of follow-up attempts failed to find a way through.
Simmonds missed the target from the edge of the box at the other end after a good cross from Kiernan on the left and Green was booked for a foul near the halfway line, before Van Sas came out of his penalty area to beat Clifton to another ball from Kiernan on 78 minutes.
Another opportunity came when Kiernan turned inside the box before finding Simmonds, although his shot was saved by the keeper.
Joel Noala came on for Mebude with eight minutes to go, with the prospect of penalties looming.
A shot by Green was blocked as Town started to get on top, then a great chance came as Smith got on the end of a Cropper long throw but he could not direct the ball into the net from close range.
Robertson was booked for bringing Green down near the halfway line, before a City break came when Borges nipped in to win the ball, skip away from Maher’s challenge and run through. He went on to find Kian Brekin but his shot was pushed away by Crocombe.
Holohan replaced Khouri and Pearson came on for Maher as the game moved into four added minutes and a Cropper long throw seconds later was deflected behind for a corner. The ball from the flag was headed clear and a City break came to an end when Clifton was pulled down.
Kiernan did well to win a corner as Town kept pushing for a winner but it was not to come as Pearson headed wide, meaning the game had to be decided from the penalty spot.
Crocombe gave Town an early advantage as he saved Charles’ attempt, with Holohan converting the home side’s first kick.
Katongo and Clifton both scored, before Bobb was also denied by Crocombe. Kiernan made it three from three for the Mariners but Robertson kept the visitors in the hunt at 3-2.
Their hopes came to an end with the next kick though, as Pearson stepped up to beat Van Sas and put Town into the draw for the first knockout round as group winners, joining Mansfield Town on five points from their three games.
Attention now switches back to league matters, with Town next in action at home to Doncaster Rovers on Saturday.