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.
Benjamin Sesko's late header set up a grandstand finish, but it proved too little, too late for Fletcher.
A red card for teenager Shea Lacey in stoppage time for dissent rounded off United's miserable afternoon.