Substitute Jordan Siebatcheu scored a stoppage-time winner to earn Young Boys a 2-1 victory over 10-man Manchester United in their Champions League opener on Tuesday.
Despite playing with 10 men for 55 minutes, it looked like a rather solid defensive display would see United come away with a point. But a late error from Jesse Lingard allowed Jordan Siebatcheu (90+5) to slot home the winner with the final kick of the game.
Man Utd had been heavy favourites heading into the game and made the perfect start as Ronaldo - who went level with Iker Casillas on all-time Champions League appearances (177) - slotted through David Von Ballmoos' legs inside 13 minutes.
In cruise control, United's task was made more difficult after fullback Aaron Wan-Bissaka was sent off for a lunging tackle on Christopher Martins with just 35 minutes on the clock.
Sensing an opportunity and buoyed by a passionate home crowd, Young Boys pressed and probed for the leveller and made the breakthrough midway through the second half. Moumi Ngamaleu (66) poked the ball past David de Gea before Siebatcheu scored a late second following continuous pressure from the hosts.
It was a nightmare start for Man Utd in Group F, who will welcome Villarreal - who beat them in the Europa League final three months ago - to Old Trafford in two weeks' time in desperate need of three points.