Manchester United manager Jose Mourinho issued a warning to his players despite returning to the Champions League with a comfortable 3-0 win against Basel.
United were largely in control at Old Trafford on Tuesday as goals from Marouane Fellaini, Romelu Lukaku and Marcus Rashford secured all three points in the Group A opener.
But, while pleased with the result, Mourinho felt they took their foot off the pedal having gone 2-0 ahead early in the second half.
"Three points is very important," the Portuguese boss told BT Sport. "It's important to win when starting at home.
"Until the second goal, we were very stable but, after that, we were not making the right decisions and we could have put ourselves in trouble.
"There were bad decisions, fantasy football, PlayStation football, tricks. I don't like it. You gamble a little bit.
"The players probably felt the game was over at 2-0, but you have to respect the opponent.
"We lost our shape, the players relaxed too much and I didn't like it. But, overall, the performance was solid and three points is the most important thing."
The victory was built around a fine display from Fellaini, who entered the game on a negative note when stand-in skipper Paul Pogba had to be withdrawn with an apparent hamstring injury.
Mourinho was unaware how serious that problem was, but suggested his other midfielders – including Fellaini – were more than capable of filling the void left by the French star.
"I haven't spoken to the medical department," he suggested. "The squad is for this. For injuries and suspensions.
"But we don't cry. If we have no Paul, we have [Ander] Herrera, [Michael] Carrick, Fellaini and [Nemanja] Matic."
On Fellaini, in particular, Mourinho added: "He is a player with special qualities who does things that some other players cannot do.
"I would say that he is one of my most important players – even if sometimes I don't start with him."
And maligned United midfielder Fellaini appreciates his manger's backing, saying: "It feels good.
"He knows what I can do and my quality. That's important for me. I give everything on the pitch."
Another player who will have impressed Mourinho is Lukaku, who netted his sixth goal in as many games for United on his Champions League debut.
The Belgium striker refused to be drawn on his own efforts, focusing on the importance of United responding to a disappointing 2-2 Premier League draw at Stoke City on Saturday.
"I was delighted with the win," he said. "We wanted to bounce back after the slip up against Stoke."
|I say one thing and you write something else - Angry Ronaldo brushes off media|
|Griezmann needs support of Atletico and fans – Simeone|
|Monaco paid for mistakes in Champions League exit - Jardim|
|We had to rely on personal pride - Berizzo praises Sevilla´s stunning comeback|
|Championship Review: Coleman loses first Sunderland game, Fulham win nine-goal thriller|
|City fans get first sight of local star they crave in Phil Foden|
|Gunes wants more after historic Besiktas Champions League qualification|
|Extra rest helped Rose shine in Dortmund – Pochettino|
|Allegri plays down Dybala-Messi comparisons|
|Zidane: We knew Ronaldo, Benzema goals would come|
|It feels like we lost - Klopp frustrated at Liverpool´s second-half collapse|
|It depends on Foden - Guardiola puts ball in teenager´s court|
|Postecoglou leaves Australia post|
|Ronaldo overtakes Messi in Champions League goalscoring race|
|Manchester City 1 Feyenoord 0: Sterling strikes late as top spot is clinched|
|Sevilla 3 Liverpool 3: Klopp´s side fail to survive Spanish inquisition|
|Borussia Dortmund 1 Tottenham 2: Son grabs winner as Spurs seal top spot|
|Napoli 3 Shakhtar Donetsk 0: Insigne stunner helps keep knockout hopes alive|
|APOEL 0 Real Madrid 6: Record-breaking Ronaldo and Benzema send holders through in style|
|Monaco 1 RB Leipzig 4: Werner brace dumps Ligue 1 champions out|
|Ronaldo breaks record for Champions League goals in a calendar year|
|I wanted to cry with Buffon - Rakitic sympathy for Italy great|
|Defiant Smalling responds to ´surprise´ England omission|
|Neuer ´on schedule´ but Heynckes won´t rush Bayern star|
|Messi contract saga not swaying Barcelona boss Valverde|
|Spartak Moscow 1 Maribor 1: Stoppage-time equaliser gives Russians everything to do at Anfield|
|Besiktas 1 Porto 1: Talisca leveller sends hosts through|
|Mkhitaryan questions leave Mourinho riled|
|Jones out of Basel, Brighton games but Mourinho hopeful on Bailly|
|Conte unhappy with Chelsea´s fixture congestion|
|Pepe tells Ronaldo: Come to Besiktas!|
|Clement expects Abraham to shake off back injury for Bournemouth clash|
|Oddo replaces sacked Del Neri at Udinese|
|Bartomeu hints at January Barcelona signings|
|Emery defends ´responsible´ Neymar from lifestyle criticism|
|Del Neri sacked by Udinese|
|Everton striker Niasse facing two-match ban after FA diving charge|
|Lampard excited by English clubs in Champions League|
|Thiago and Coman back for Bayern´s trip to Anderlecht|
|Dybala hails Messi as ´our Maradona´, wants to play with Neymar|
|Sherwood talks up Spurs as potential Champions League winners|
|Borussia Dortmund on the brink as Real Madrid eye progress - Champions League in Opta numbers|
|Hughton hopeful on video assistance after Brighton denied penalty|
|Klopp staying calm over Salah form|
|Griezmann: I don´t regret staying at Atletico|
|Guardiola dismisses Champions League favourites tag|
|Brighton and Hove Albion 2 Stoke City 2: Gross, Izquierdo extend home unbeaten run|
|Rose in contention to face Dortmund as Pochettino denies ´issue´ with defender|
|Benzema knows he can give more – Zidane|
|I´ve fulfilled my dreams already – Klopp has no plans to coach Barcelona|
|Aubameyang will face Tottenham, Bosz confirms|
|Klopp expects Matip to face Chelsea, Lallana return getting ´nearer´|
|Berizzo looking to former Red Aspas to provide lessons for Sevilla|
|Mangala ready to pounce, but realistic on Man City playing time|
|Mendy injury means Aguero or Jesus for Guardiola|
|Guardiola sends ´big hug´ to ´amazing, so gentle´ Pulis|
|Tavecchio quits as head of FIGC, claims board have refused to resign|
|Benedetto facing Argentina World Cup KO with cruciate injury|
|Shape up! Heynckes reveals demand to Bayern star Vidal|
|Ramos sits out Madrid trip to APOEL|
|West Brom sack Pulis after wretched run|
|Lloris wants Spurs to forget title and focus on top four|
|Pogba no Gerrard yet, says Benitez|
|Guardiola will ´kill´ City stars if they get complacent|
|Ibrahimovic: My injury was worse than people know|
|Icardi like a ´raptor pouncing on its prey´, says Spalletti|