Cristiano Ronaldo, who equalled Iker Casillas’ Champions League appearance record of 177 matches, started upfront for United. Raphael Varane, Nemanja Matic and Mason Greenwood all dropped to the bench, with Victor Lindelof, Fred and Donny Van de Beek coming in.

Both sides created chances in the opening four minutes. First from the home side’s Meschak Elia, then Bruno Fernandes almost found Jadon Sancho in the box but goalkeeper Von Ballmoos did well. However, Ronaldo opened the scoring when Fernandes’ beautiful pass found the Portuguese talisman who slotted the ball past the keeper.

In a turn of events, Manchester United right-back Bissaka was shown a straight red card in the 35th minute after a careless, studs-up challenge on Martins. Moments later, Young Boys almost equalised when Ulisses Garcia’s cross flashed through the area and found Fassnecht. However, his fierce volley dragged just inches wide of the far post.

With Young Boys pushing for the equaliser, United needed to regroup at half-time and introduced Raphael Varane for the second half. The home side kept pushing for the equaliser, creating numerous chances in the process as they dominated the midfield. Ronaldo was isolated up front and received little support.

Young Boys made a deserved breakthrough in the 66th minute when Elia sent in a  cross from the right, with Nicolas Ngamaleu poking a foot in front of Varane and flicking the ball past De Gea at the near post.

The hosts continued to push for a winner as the fans roared them on. Sandro Lauper forced a fingertip save from De Gea. The Manchester United keeper expertly saved to keep his side in the game.

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However, a costly error from Jessie Lingered in the final minutes put Young Boys ahead. A sloppy pass from the substitute left Siebatcheu through on goal, and he easily fired the ball past the helpless De Gea to send the fans into a frenzy.

It was a nightmare start for Manchester  United in Group F, who will welcome Villarreal to Old Trafford in the next Champions League encounter in desperate need of three points. Villarreal beat them in the Europa League final three months ago.

“We’ve won a couple of games already, but to beat Manchester United in the Champions League is unique,” Young Boys manager David Wagner said. “I’m just really happy for everyone who witnessed it. Every single person here played their part.”

“The lads went above and beyond their limits. That’s only possible with great support. We wanted to show our intensity, our aggression and our passion. The lads did brilliantly and deserve huge credit,” Wagner added.

Manchester Utd are back in action on Super when they travel to West Ham. Their next Champions League game will come at home to Villarreal on Wednesday September 29.

UEFA Champions League results

Barcelona 0-3 Bayern Munich

Dynamo Kyiv 0-0 Benfica

Young Boys 2-1 Manchester United

Villarreal 2-2 Atalanta

Sevilla 1-1 Salzburg

Lille 0-0 Wolfsburg

Chelsea 1-0 Zenith St. Petersburg

Malmoe FF 0-3 Juventus

Chidi Nwoke/UEFA.