Despite the disappointing result, Mourinho found something to be happy about - the performance of £30m summer signing Bailly.
He said: "We can speak about Eric Bailly, who was playing for Villarreal who never played in a derby of this dimension, but was our best player, was the player of the month, and produced a fantastic performance. He coped with many situations.
“So you never know the way players are going to react, especially when you don't know them so well.
“And after only a couple of months it is too early to know them really well."