Manchester United remain without a win this season after crashing out of the Carabao Cup at Grimsby Town in a huge giant-killing upset despite hitting back from 2-0 down to force a penalty shoot-out at a saturated Blundell Park.
The League Two side last faced United in a competitive match in 1948, but did not look out of place against the Premier League visitors in the second-round clash with Charles Vernam (22′) and Tyrell Warren (30′) giving them a merited 2-0 half-time lead.
United manager Ruben Amorim made a triple change at the break with Matthijs de Ligt, Bruno Fernandes and Bryan Mbeumo introduced as they tried to avoid an early exit and was it the former Brentford forward Mbeumo who gave them hope with a deflected finish on 75 minutes.
With the clock ticking down and Grimsby clearly tiring, Harry Maguire popped up to force the header into the net on 89 minutes from a Mason Mount corner.
United had the chance to win it 5-4 on penalties after Andre Onana, who was badly at fault after missing a cross as Warren scored his side’s second, halted Clarke Oduor’s penalty.
But home goalkeeper Christy Pym saved from Matheus Cunha before fellow new United arrival Mbeumo hit the bar trailing 12-11 after slotting his first spot kick.
It was probably a justified victory for the Mariners, who could have been 3-0 ahead with replays suggesting Cameron Gardner was also onside after seeing a goal disallowed on 70 minutes.
