Mourinho made 10 changes in midweek for the 2-0 Capital One Cup win over Arsenal and Juan Mata put down a marker for a start at St James' Park with an excellent display that was rounded off by the second goal.
The Chelsea boss said: "It's not easy for me to leave some players on the bench because everybody deserves to play.
"To have all these choices is a good problem with all the players doing well. To be the responsible man to say 'you don't play, you are not selected, you go to the bench, you go to the stand'. In this moment it is very hard because I feel I am unfair with all of them.
"The ones I am not selecting, I am unfair with them because they are doing everything to play.
"I change the team and people come and play a magnificent match so it is a difficult feeling for me because I'm unfair with some of them.
Mourinho is refusing to take credit for the revival of Fernando Torres who scored his first league goal of the season against Manchester City last weekend and looks a new player under the Chelsea manager.
"I did nothing, I do what I always do trying to get the best out of my players.
"Fernando is responsible for his self-motivation, his self- commitment.
"I don't like this history that one day the player is a disaster and the next day the player is phenomenal.
"I don't think Fernando is a kid to be influenced by these wins, I want him to be stable and not to be too much worried by proving himself or not proving himself, scoring or not scoring."