Manchester United are on the brink of an early exit from the Champions League after blowing a 2-0 lead to lose 4-3 on Wednesday to FC Copenhagen as Marcus Rashford was sent-off in the Danish capital.
Rasmus Hojlund looked to have come back to haunt his former club by scoring twice inside half an hour.
But Rashford's sending-off swung the destiny of the match and possibly sealed United's fate with a third defeat in four games in Group A.
Mohamed Elyounoussi and Diogo Goncalves from the penalty spot levelled for Copenhagen before half-time.
Bruno Fernandes' spot-kick briefly put United back in front, but two goals in the final seven minutes from Lukas Lerager and 17-year-old Roony Bardghji handed Copenhagen their first Champions League win since 2016.
United sink to the bottom of the group, one point behind Galatasaray and Copenhagen, with two games left to play.
The Red Devils travel to Galatasaray in three weeks' time before hosting runaway group winners Bayern Munich.
Defeat will again ramp up the pressure on United boss Erik ten Hag as a disastrous start to the season in both the Premier and Champions League goes on.
But the Dutchman will reflect on what might have been but for Rashford's dismissal after an excellent opening half an hour.
Copenhagen boss Jacob Neestrup claimed United would be met with an atmosphere "100 times" more intense than his side faced at Old Trafford two weeks ago.
But the locals were quickly quietened by one of their own inside three minutes.
Hojlund is still to score his first Premier League goal since a £64 million ($78 million) move from Atalanta but is now the joint top scorer in the Champions League this season with five in four games.
He could not miss after being picked out by Scott McTominay at the back post for a tap in after a fine team move to open the scoring.
Hojlund was again in the right place for a simple finish to make it 2-0 after Kamil Grabara parried Alejandro Garnacho's initial effort.
Grabara then needed to make a fine save to deny Hojlund a first half hat-trick.
However, the momentum completely swung when Rashford's difficult season took another turn for the worse.
There appeared no malice from the England international, but his studs caught Elias Jelert on the ankle as he tried to protect the ball and after a VAR review he was shown red.
From the resulting free-kick, Bruno Fernandes flicked a header off his own crossbar.
But United were not handed a reprieve for long as Elyounoussi turned in Goncalves' clever ball back across goal.
Thirteen minutes were added at the end of the first half due to an earlier delay caused by a medical emergency in the stands and United's lead did not survive until the break.
Andre Onana saved Jordan Larsson's penalty in the last action of the game in United's 1-0 win when the sides last met.
Goncalves had been withdrawn by that stage a fortnight ago, but he took responsibility from the spot and coolly sent Onana the wrong way.
The roles were reversed as VAR came to United's rescue in the second half to penalise a handball by Denis Vavro and Fernandes emphatically smashed home the resulting penalty.
The visitors, though, failed to hold out for a vital three points.
Diogo Dalot was caught napping as Lerager stole in at the far post to bundle the ball past Onana to give Copenhagen fresh hope.
Teenage substitute Bardghji then produced a fairytale finish for the hosts as he smashed a volley into the ground and beyond Onana after Maguire failed to clear a cross into the box.
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