Scott McTominay scored a stoppage time brace to turn around Manchester United's fortunes after being a goal behind against Brentford for most of the match.
Mathias Jensen put the visitors ahead at Old Trafford, and with the hosts struggling to convert their chances, it looked like Erik ten Hag's side were facing a third straight home defeat.
But McTominay came off the bench and was able to strike twice in stoppage time to save Man United's blushes - and condemn Thomas Frank's Bees to a cruel defeat.