The defender, signed from Villarreal in June, has made a powerful start to life at Old Trafford, claiming the Player of the Month award for August following a series of blockbuster displays at the back.
And even in what turned out to be a forgettable afternoon against Man City, the Ivorian was an indomitable force at the back.
Speaking after the game, Mourinho made it clear that the 22-year-old’s performance didn’t go unnoticed.
“We can speak about Eric Bailly, who was playing for Villareal 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 said.
“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.”
The first-half of the derby saw Pep Guardiola’s side mount a practically uninterrupted onslaught, tearing through Man United’s midfield with reckless abandon. And if it wasn’t for the barbaric exploits of Bailly, the game could have been settled by half time.
And with United furiously throwing bodies forward in the second half, the Ivorian vigorously thwarted numerous counter-attacks, even making one stunning goal-line block with a mixture of his face and chest. He may be disappointed with the result, but Bailly can take great confidence for his performance against a rampant City attack.