Key stats
- Man Utd have lost their 100% progression rate in the League Cup when facing teams from the fourth tier of English football. Before facing Grimsby they beat Colchester 3-0 in the 2019/20 quarter-finals.
- Grimsby Town had previously lost their last three League Cup ties against sides from a higher division, losing the three games by an aggregate score of 15-2.
- It was the first meeting between Grimsby Town and Man Utd since the 1947/48 top-flight campaign – the Mariners won 4-3 at Old Trafford and drew 1-1 at Blundell Park that season.
Highlights
Analysis
Andre Onana had a difficult game once again for Man Utd and scored a rating of 5.8 - just 0.1 behind new signing Benjamin Sesko, while Charles Vernam starred for the League Two side.
Match report
League Two side Grimsby led 2-0 with just 15 minutes to play thanks to goals from Charles Vernam and Tyrell Warren.
Bryan Mbeumo had sparked a late rally from the Red Devils with his first goal for the club, but the Cameroonian missed the decisive spot-kick to pile more pressure on under-fire United boss Ruben Amorim.
The Portuguese coach was already facing scrutiny after a winless start to United's Premier League season.
The 20-time English champions finished 15th last season in their worst league campaign since being relegated in 1974.
Now one of their only two realistic shots at a trophy this season has disappeared in one of the worst results in the club's history.
Amorim made eight changes from the side that drew 1-1 at Fulham on Sunday, but still named a side that cost hundreds of millions of pounds, packed full of internationals.
Benjamin Sesko made his first United start after a £74 million move from RB Leipzig, while Andre Onana returned on a night to forget for the United goalkeeper.
Grimsby had been waiting for a visit from United since 1948 and roared out the blocks to fully deserve their two-goal half-time lead.
Vernam fired a low powerful effort past Onana at his near post on 22 minutes to the delight of most of the 9,000 capacity crowd at Blundell Park.
The hosts continued to make a mockery of the three-division gap between the sides.
Cameron Gardner had the ball in the net but was denied a second for a handball.
Yet, moments later Grimsby did double their lead when Onana failed to claim a corner and Warren gratefully tapped in.
Onana's poor evening may hasten United's rumoured move for Belgian goalkeeper Senne Lammens in the final days of the transfer window.
Amorim responded at half-time by throwing on captain Bruno Fernandes, Mbeumo and Matthijs de Ligt for a rescue mission.
Despite United's dominance of the second period, they were lacking inspiration until Mbeumo took aim and curled into the bottom corner from outside the box.
Harry Maguire has been forced forward as a makeshift striker at times during Amorim's troubled reign and looked to have come up with a huge moment for his manager in the 89th minute as the England international headed in Mason Mount's corner.
Sesko then skied an incredible chance to win the tie five minutes into stoppage time, ensuring penalties were needed.
Matheus Cunha had the chance to win the shootout at 4-4, but his effort was saved by Christy Pym.
After 15 more successful spot-kicks, including from both goalkeepers, Mbeumo hit the bar to seal United's fate.
Click here to see all the stats of the match.
Post-match reaction
Man Utd manager Ruben Amorim told Sky Sports: "In the end, it doesn't matter if we recover or not, it's the signs the team gave during the game, the beginning of the game.
"I think the best team won, the only team that was on the pitch. The best players lose because one team can win against any group of players, and I think the team and the players spoke really loud today, so that's it. We lost, the best team won.
"The way we start the game without any intensity, all the idea of the pressure, we were completely lost and that's why I think they spoke really loud."
Grimsby Town boss David Artell told ITV: "This is an accumulation of 15 months, 18 months, all encompassed in one night. Look, they're an unbelievable team, Manchester United. They've got an unbelievable manager and they're on the right track, you can see that.
"We've got an unbelievable group of players as well, who want to play for this football club, live in the area and want to get better every day."