The United boss took on his former side but watched on in dispair as the Blues romped to victory.
Pedro, Gary Cahill, Eden Hazard and N’Golo Kante were all on target as Chelsea inflicted Mourinho’s biggest defeat in the Premier League.
And he’s taken full responsibility for the result.
“I have to apologise for that as the leader of this dressing room”
Jose Mourinho’s message to Man United’s fans after their defeat at Chelsea
“The millions of the fans that we have all around the world, they are obviously with a very bad feeling,” he told MUTV.
“I feel so sorry for that. I have to apologise for that as the leader of this dressing room, and the only thing I can say is that I am Man United 100 per cent.
“Not 99 per cent and one per cent for Chelsea or for any other club, I am 100 per cent for Man United.
“And because of that I feel deeply at the situation, but there is only one answer, like I was telling the players – training tomorrow, and keep fighting.”
Man United have a chance to get back to winning ways in the EFL Cup on Wednesday.
But they’ll have their work cut out with Pep Guardiola’s Manchester City their opponents.