Manchester United manager Jose Mourinho revealed on Thursday night that his players were cracking so many jokes in the dressing room before the Europa League tie with Saint Etienne that he knew they were going to be off their game when the match began.

Mourinho marched off for the half-time dressing room before the whistle was blown after an opening 45 minutes which he said was “so bad”. After the game he sounded a warning to his players that there would be teams of Champions League class waiting in the next round if, as expected, United’s 3-0 first leg win proves to be enough. Roma, Shakhtar Donetsk, Fiorentina and Lyons all enjoyed first-leg wins.

“I had the feeling immediately in the dressing room,” Mourinho said. “Too noisy. Too funny. Too relaxed. My assistants had the feeling in the warm-up, some of the guys were not really focussed and not having the right adrenalin in their bodies.” The Portuguese was appalled by an early poor Eric Bailly back pass that put Sergio Romero under pressure. He removed Marouane Fellaini at half time, sent on Jesse Lingard, and United improved after the interval, playing with more pace.

They were fortunate, with two of Zlatan Ibrahimovic’s three goals coming after a soft free kick and penalty which he won and scored from. “Zlatan is just doing his job, he’s a striker and goalscorer,” Saint Etienne manager Chrisophe Galtier said afterwards. “But despite his talent he was given favourable conditions to score his goals and help him on his way to that hat-trick.”

Mourinho - who will be without suspended Ander Herrera in France next Wednesday - said his players had to approach this competition with the same seriousness they apply to the Champions League.

“I know Champions League is a competition that everyone wants to play and win but we don’t play Champions League; we play Europa League,” he reflected.

He said there had been a little of the same complacency at times in the group stage. “But when we needed to win, we did it. We needed to win against Fenerbahce and did it, needed to win on the last night in Ukraine and did it. When focus is there we answer. Tonight I think first half was too relaxed. Saint Etienne had right intensity and created us problems.”

Manchester United vs Saint-Etienne player ratings Show all 11 1 /11 Manchester United vs Saint-Etienne player ratings Manchester United vs Saint-Etienne player ratings Sergio Romero - 6 out of 10 Endured an early scare following Eric Bailly's botched clearance but settled into the game and became more assured as time wore on. Manchester United vs Saint-Etienne player ratings Antonio Valencia - 6 Nearly scored to end a three-year drought - but it wasn't to be. Got well forward, though some of his deliveries could have been better. Respectable evening in all. Manchester United vs Saint-Etienne player ratings Eric Bailly - 6 Made one important block early on but his decision-making was found wanting on occasion. Improved as the game went on. Manchester United vs Saint-Etienne player ratings Chris Smalling - 6 Didn't look too assured at times, allowing a number of Saint-Etienne runs in behind. Strong in the air though. Manchester United vs Saint-Etienne player ratings Daley Blind - 5 Poor tracking nearly handed the visitors an equaliser in the second half. Somewhat shaky. Manchester United vs Saint-Etienne player ratings Marouane Fellaini - 4 Not the best of games for the Belgian. Struggled to have much say and was subsequently substituted at half-time. Manchester United vs Saint-Etienne player ratings Ander Herrera - 6 Kept United ticking over in the centre of the park. Recycled well and created chances for the home side. Solid evening for the midfielder. Manchester United vs Saint-Etienne player ratings Paul Pogba - 7 Strong both on and off the ball. Showed his worth with real moments of pure class and equally impressive in his defensive duties. Should have converted his headed effort though. Manchester United vs Saint-Etienne player ratings Juan Mata - 7 Rounded and comfortable evening for the Spaniard. Offered a reliable source of service to his team-mates and even managed to make a number of runs in behind the opponents' defence. Manchester United vs Saint-Etienne player ratings Zlatan Ibrahimovic - 7 His hat-trick secured victory for the home side. Lady Luck helped him in his first and it was a case of right time, right place for the second. Took his penalty with ease and provided a general source of threat throughout. Manchester United vs Saint-Etienne player ratings Anthony Martial - 7 Looked busy all night long. A real menace down the flanks and threatened in and around the Saint-Etienne box. Positive, energetic performance.

Mourinho claimed he would not be tempted to rest too many players in Saint Etienne. “I always respect football,” he said. “It can be nasty with you, I don’t want my tem to be punished so I will go with a strong team.