United interim boss Darren Fletcher could only watch on in horror as the Red Devils' last chance of silverware this season and likely his chances of landing the job until the end of the season went up in smoke at Old Trafford.
Fletcher's men were left to rue not making more of a positive start before Brajan Gruda fired the visitors in front on 12 minutes from Danny Welbeck's cross.
The roles were reversed midway through the second half as Welbeck lashed into the top corner against his former club.
There were persistent chants targeting United co-owners the Glazer family and British billionaire Jim Ratcliffe as the discontent at Old Trafford grew.
And any hope those in charge of the club had for a bounce following the removal of Ruben Amorim has proved very short-lived.
United will play only 40 games this season after exiting both domestic cup competitions at the first hurdle -- their lowest number since 1915.
"I think you could see the players are fragile but they've got to respond," said Fletcher.
"This team is still good enough to achieve success this season but they have to dig deep."
Benjamin Sesko's late header set up a grandstand finish, but a red card for teenager Shea Lacey in stoppage time for dissent rounded off United's miserable afternoon.