Mocking Manchester United from the stands and teasing them with inflatable haddocks, fans delighted in Grimsby Town’s triumph over this once illustrious football club. It was an unforgettable night for Grimsby and one that left spectators basking in the latest downfall of the well-known team.

The Blundell Park locals cherished every moment, and rightfully so. This was a landmark victory for the League Two side in a remarkable Carabao Cup match, which is sure to be remembered in Cleethorpes’ history.

But where does Manchester United go from here, after such a dismal display? The hopeful spirit following a summer of rebuilding and substantial investments under Ruben Amorim had already diminished after two lackluster Premier League games, and now this setback further dents their season.

United’s first-ever cup defeat to fourth-tier opposition will take its place alongside Bournemouth, York City and Southend in the hall of shame.

Amorim did make lineup adjustments, yet the squad was still worth £400million, even with academy talents like Kobbie Mainoo and Tyler Fredricson included at no cost.

The harsh reality for United and their disappointed fans is that Grimsby truly earned their victory. The two teams hadn’t faced each other in 77 years, highlighting the gulf between them in recent football status.

Still, some credit is due to United for bouncing back from a two-goal deficit to force an extended penalty shootout, with Bryan Mbeumo marking his first goal for the club after a £71million transfer from Brentford, and Harry Maguire equalizing in the 89th minute with a header.

But after Andre Onana looked to have redeemed himself with a one-handed save from Clarke Oduor, two of United’s three big summer signings failed from the spot as Amorim spent the entire shootout hunkered down in the dugout unwilling to watch.

Grimsby goalkeeper and boyhood United fan Christy Pym saved from Matheus Cunha. Then as we moved into a second round of penalties after both keepers converted, Mbeumo sent the 26th attempt against the underside of the bar and Blundell Park into delirium.

As United look to clear the decks of fringe players before Monday’s transfer deadline, Alejandro Garnacho, Antony, Jadon Sancho, Rasmus Hojlund and Tyrell Malacia probably can’t wait to get out the place and away from this never-ending circus as fast as possible.

And then there’s Mainoo who got the chance he wanted here at probably wishes he hadn’t.

If Mainoo’s first game of the season turns out to be the last of a United career that promised so much, then what a depressing way to go out.

It felt like a big night for Sesko too on his full debut after a big-money move from RB Leipzig and two rather subdued appearances off the bench against Arsenal and Fulham. The Slovenian was largely anonymous and then curiously chose to be the last outfield player to step up in the shootout. Not exactly the kind of confidence you expect from a £74m striker.

Meanwhile, Onana’s summer has been disrupted by a hamstring injury that allowed Altay Bayindir to take over as No.1, however temporarily, and speculation over his future has not been helped by the club’s attempts to sign Senne Lammens from Antwerp.

With Bayindir struggling in the opening two games, particularly under set-pieces, this was Onana’s chance to reassert his authority and yet he was picking the ball out of the net twice in the opening half an hour.

Could he have done better with the first goal? Possibly. United had come under early pressure and struggled to weather it when Darragh Burns switched played from right to left.

Charles Vernam controlled it with one touch and still had enough time to size up a shot which he rifled inside the near post as Onana failed to keep it out.

At that point, Cameron Gardner had already headed straight at the United keeper who had also been forced to turn Vernam’s corner over his own bar, looking every bit as uncomfortable as Bayindir.

That was nothing compared to Grimsby’s second goal which came seconds after another effort was ruled out because it went in off Gardner’s arm.

Onana came out to claim a cross from the left but flapped and barely made contact with the ball, gifting Tyrell Warren an opportunity to tap it into an empty net.

The Grimsby fans could barely believe what they were seeing. Light-hearted chants of ‘we only sing when we’re fishing’ turned to a chorus of ‘sacked in the morning’ as Amorim paced up and down the technical area in a state of equal incredulity.

His team rarely looked like getting themselves back into the game in a disastrous first half.

Amorim had no choice but to send for some big guns at half-time, sending on Bruno Fernandes, Matthijs de Ligt and Mbeumo to provide some stability and leadership.

Pym made a fantastic save low to his left to keeper Fernandes’ shot from range but United’s first-choice front three of Mbeumo, Sesko and Cunha struggled to lay a glove on a fantastic Grimsby defence until Mbeumo pulled one back, firing low into the corner after an impressive run and Maguire powered in a header from Mason Mount’s corner to set up the late drama.