Eden Hazard’s woeful missed penalty six minutes from time meant they could only return from Slovenia with a draw thanks to Nemanja Matic’s equaliser.
Maribor had deservedly taken the lead against the sleepy Blues when Agim Ibraimi brilliantly curled in from the edge of the box.
And Mourinho admitted he must take the blame for his team’s poor focus against a side they thrashed 6-0 just two weeks ago.
“I was conscious of it, but I was not successful in passing over that message,” said the Chelsea boss.
“If I can’t convince the players that the game is difficult and you have to play from minute one, obviously it’s my responsibility.
“Many times surprises happen when people are not fully focused, when they believe the game can’t be a difficult one.
“We had played very slow and with no intensity, no creativity. It was easy for Maribor to control the game
“Only when Maribor scored did the players realise the game was in danger. After that, it was a fantastic reaction.”