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around a fine display from Fellaini, who entered the game on a negative note when stand-in skipper Paul Pogba had to be withdrawn with an apparent hamstring injury.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."
|Barcelona boss Valverde tells Chelsea: History counts|
|Schmidt departs as Wolfsburg face relegation fight|
|Madrid, Barca & PSG are Champions League favourites, says Heynckes|
|Former football coach Bennell sentenced to 31 years|
|Hummels wary of ´top European team´ as Bayern prepare for Besiktas|
|WATCH: ´Crazy´ Evra drives to West Ham training in London cab|
|Barca clash a chance for Chelsea ´to do things right´, proclaims Rudiger|
|Lucas claims Tottenham can win Champions League|
|Barcelona tie will not decide Conte´s Chelsea future, says Deco|
|Lewandowski won´t be distracted by Real Madrid rumours|
|Man Utd must not underestimate Sevilla - Navas|
|Iniesta will not be made welcome at Stamford Bridge, warns Azpilicueta|
|Ballack sees ´a big difference´ between Bundesliga and Premier League|
|Betis boss would have preferred to face Madrid´s BBC|
|Chelsea v Barcelona: Messi´s blues against the Blues|
|James leaving Madrid was the best thing, says father|
|He´s looking good – Zidane thrilled with Ronaldo|
|It needs to take 30 seconds – Matic wants quicker VAR|
|Gattuso: My job is to be the players´ nightmare until season´s end|
|I wasn´t good enough – Guardiola reveals Wigan rejection|
|Brazilian derby between Vitoria and Bahia abandoned after red-card frenzy|
|It was crazy, but I like that - Zidane revels in eight-goal Betis thriller|
|Asensio credits Zidane for Madrid´s thrilling Betis comeback|
|Zidane hopeful over Marcelo hamstring injury|
|Bonaventura claims Milan can catch Inter|
|Bravo for Claudio! Guardiola to pick keeper at Wembley|
|Mourinho hoping for reinforcements at Sevilla|
|Real Madrid become first side to score 6,000 goals in LaLiga|
|Real Betis 3 Real Madrid 5: Asensio at the double in LaLiga classic|
|AC Milan 1 Sampdoria 0: Bonaventura makes it 10 unbeaten for Rossoneri|
|Schurrle excited to finally link up with Reus and Gotze|
|Real Madrid defender Marcelo suffers hamstring injury|
|Costa fumes referees ´want to give me a card´, but Simeone plays down penalty row|
|Stoger makes Dortmund history with Gladbach win|
|Championship Review: Leeds fight back for point, Norwich & Ipswich share derby spoils|
|Borussia Monchengladbach 0 Borussia Dortmund 1: Burki unbeatable as Reus returns to haunt Foals|
|FA Cup ´magic´ no surprise to Pochettino after Rochdale thriller|
|Rochdale hero Davies: This is every kid´s dream|
|Atletico Madrid will not stop in pursuit of Barcelona, promises Gameiro|
|´Wrong image´ to blame for VAR confusion in Manchester United´s FA Cup win|
|Rochdale 2 Tottenham 2: Davies denies Kane in FA Cup classic|
|Atletico Madrid 2 Athletic Bilbao 0: Gameiro and Costa settle cagey clash|
|Napoli set club record with another Serie A win|
|Napoli 1 SPAL 0: Allan sends hosts top of Serie A again|
|Allegri allays Higuain injury fears|
|Allegri convinced Juve can get past Spurs|
|Everton fear ´long-term´ injury for Mangala|
|If it isn´t Madrid, it´s Paris - Hazard tires of speculation|
|Torino 0 Juventus 1: Champions win derby but lose Higuain|
|Neymar exit made Barcelona stronger - Ter Stegen|
|Injured Higuain forced off against Torino|
|Jesus confident of returning strong after knee injury|
|We had to change hotels – Ovrebo recalls fury after 2009 Chelsea-Barcelona semi-final|
|Spalletti: Inter board will decide my future|
|Fabregas still wary of timeless Iniesta|
|Liverpool´s 30-goal hero Salah: There´s more to come|
|Valverde: Coutinho dropped for the good of Barcelona|
|Ronaldo better than Neymar? No says Xavi|
|Real Madrid hurt you with nothing – Xavi says PSG loss an injustice|
|Conte: Chelsea need perfect game to stop Messi and Barcelona|
|Inter in a fragile moment, says Spalletti|
|Booed Emery praises PSG´s mental strength|
|Cavani hails ´good reaction´ as PSG bounce back in style|
|Mourinho wants referees to have final say on VAR|
|Genoa 2 Inter 0: Pandev piles misery on old employers|
|Manchester United to host Brighton in FA Cup quarter-finals|
|Mata ´still up for VAR´ despite disallowed goal at Huddersfield|
|Valverde: Barcelona had to suffer at Eibar|
|Championship Review: Fulham end Villa run, Cardiff pounce|
|Huddersfield Town 0 Manchester United 2: Lukaku sends visitors through after VAR controversy|
|Bayern Munich boss Heynckes hails game-changing Muller|
|Locadia benefiting from ´competitive´ Brighton - Hughton|
|Baby on board? Alba dedicates Barca goal to girlfriend|
|West Brom future ´not a decision for me´, says Pardew|
|Paris Saint-Germain 5 Strasbourg 2: Cavani at the double in bounce-back win|
|Bar-celona! Messi posts unwanted record|
|Barca go 31 LaLiga games unbeaten to tie club record|
|Mourinho: I don´t know and I don´t care when Pogba returns|
|Brighton and Hove Albion 3 Coventry City 1: Locadia, Ulloa lead Seagulls to quarter-finals|
|EIbar 0 Barcelona 2: Suarez and Alba seal points as Orellana sees red|
|West Brom 1 Southampton 2: Rondon stunner in vain as Baggies drop out|
|Wolfsburg 1 Bayern Munich 2: Lewandowski spot-on after Robben´s penalty miss|
|I hope Cutrone finds a beautiful girlfriend so he can rest and make love - Gattuso|
|Allegri denies Champions League ´obsession´ ahead of Turin derby|
|Barry, Evans start for West Brom after training camp incident|
|Sheffield Wednesday 0 Swansea City 0: Carvalhal settles for replay on Hillsborough return|
|Management ´tiring´ but Zidane not ready to leave Madrid just yet|
|Thiago back for Bayern as Heynckes rests stars for Besiktas|
|Simeone urges Atletico fans to get behind Griezmann|
|Robben amazed by Guardiola´s impact at Manchester City|
|Pogba out of Man Utd´s Huddersfield trip with illness|
|A-League Review: Perth ´Panenka´ punished, 10-man Adelaide rescue late draw|
|Robben targets two more years at the ´highest level´|
|Rashford and Herrera ´have a chance´ of making Sevilla trip|
|Emery defends PSG star Neymar after Madrid display|
|Mahrez saga now over, says Leicester boss Puel|
|Alonso to return for Barca clash but Bakayoko set to miss first leg – Conte|
|Mourinho: Manchester United will sign a midfielder|