Marcus Rashford brought them level 26 minutes later, just after Fred had avoided a red card despite appearing to headbutt PSG’s Leandro Paredes.
After consultation with VAR, the referee somehow decided to only brandish the Brazilian a yellow card.
Nevertheless, the hosts got their comeuppance in the second half, as with 20 minutes remaining Marquinhos edged PSG in front again while seemingly in an offside position.
The VAR check was a brief one despite the apparent offside claim, meaning what proved a winning strike for Thomas Tuchel's side was allowed to stand.
And just a minute later United’s evening went from bad to worse, as this time Fred was given his marching orders for a challenge on ex-United man Ander Herrera - even though replays showed him winning the ball.
However, the midfielder can’t have many complaints having avoided what surely should have been a straight red card for his altercation with Paredes in the first half.
United legend Rio Ferdinand felt he was fortunate to avoid a sending off, saying in the BT Sport studio at half-time: “He's a lucky boy not to be off the pitch. I think there's been a few occasions in the first half where he could have had a yellow card.
“Obviously the headbutt. He moves his head and motions towards the player. He makes a meal of it, yes, but in today's game he's lucky to be on that pitch.”
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Paul Scholes added: “He's very lucky. He needs to think about staying quiet. Ole might even think about taking him off.”
United are level on nine points with both PSG and RB Leipzig at the top of Group H heading into their crucial final outing against the Bundesliga club next week.