WATCH a FULL REPLAY of Young Boys v Manchester United at 7am AEST Thursday, on beIN 2 via MUTV

United appeared set for a routine victory in Berne when Ronaldo, who had scored twice on his second debut for the club against Newcastle United on Sunday (AEST), put it ahead in the 13th minute.

But Aaron Wan-Bissaka's red card late in the first half gave Young Boys hope, which was realised when Nicolas Moumi Ngamaleu levelled matters with a 66th-minute strike.

Ole Gunnar Solskjaer's men looked set to emerge with a creditable point having defended for close to an hour a man down, yet there was a remarkable late twist as Jesse Lingard misjudged a back-pass and Jordan Siebatcheu slotted past David de Gea to secure a famous result for the Swiss side.

Ronaldo squeaked the opener through the legs of David von Ballmoos, who could not prevent the ball crossing the line after the Portugal star latched on unmarked to a superb delivery with the outside of the boot from compatriot Bruno Fernandes.

Von Ballmoos fared better second time around to deny Ronaldo at his near post at the end of a quick counter, with David de Gea forced into a diving save from Christian Fassnacht's long-range effort moments earlier.

But the complexion of the game was altered in the 35th minute when referee Francois Letexier had no hesitation in showing Wan-Bissaka a straight red card for going over the top of the ball and catching Christopher Martins Pereira on the ankle.

Jadon Sancho was replaced by Diogo Dalot to fill the void left in United's defence, which coped well until under persistent pressure until Ngamaleu poked home at the near post from Silvan Hefti's low right-wing delivery.

United appeared poised to escape with a point but Lingard's loss of composure presented Siebatcheu with a simple finish to send the Wankdorf Stadium into delirium with the final kick.