United won the last-32 first leg at Old Trafford thanks to a Zlatan Ibrahimovic hat-trick, but the hosts survived some nervy moments, particularly in the first half.
When asked about the game afterwards, Mourinho admitted he was pleased with the result but was not so happy with his team’s focus in the build-up and during the clash.
Asked if he was happy with the scoreline, the Red Devils boss said:
“I am – especially because in the first half, we played so bad, and we managed to finish it winning 1-0 when we don’t deserve.
“It was down to lack of concentration.
“I had the feeling immediately in the dressing room – too noisy, too funny, too relaxed. Then my assistants had the feeling in the warm-up, with some of the guys not really focused on getting the right adrenaline in their bodies.
“Then the game started and the first thing we did was a back-pass [by Eric Bailly] to the striker [Romain Hamouma] to be face-to-face with Sergio [Romero].
“So, lack of concentration. And when you don’t have it, it’s difficult to recover it. So the first half was hard.
“Even myself on the touchline, I felt it was difficult, the communication. I needed the half-time. So we were lucky, yes, to be winning 1-0.
“I am not happy with it. At half-time, the result could be 1-1. I always think we have to play every game with the same attitude.”
Put to him that the attitude might be down to the fact it was the Europa League rather than the Champions League, Mourinho said:
“I know Champions League is the competition everyone wants to play, everyone wants to win, I know that.
“But we don’t play Champions League, we play Europa League.
“I think in the first half, it was too relaxed. Then, St Etienne were in the game with the right attitude and intensity, and they created problems.
“We don’t play Champions League, so if that is the case I would prefer to play in the Europa League than be at home watching TV. So I think with the players it is the same.”
Mourinho did stress the second half was “a different story” and said of the match overall:
“To score three goals and not concede in the first leg at home, it’s always a good result – it is not over, but it is a good result.”
And he added:
“I think if we progress and if we beat St Etienne and go into last 16, then the people will have the right attitude. Lots of good teams are going to be in the next round.
“Big teams are there, Champions League teams’ level will be there. So let’s do next time the right result, let’s go for the next draw and I think the motivation will come.”