Referee Michael Oliver was surrounded by several United players after Ander Herrera sent off for a second yellow card after two ill-judged tackles on Chelsea forward Eden Hazard.
United manager Jose Mourinho, returning to the club where he won seven major trophies, and Chelsea's Italian coach Antonio Conte also had to be separated after an angry exchange shortly after the sending off.
(Reporting by Alan Baldwin, Editing by Ken Ferris)
