Arsene Wenger accused his Arsenal team of being "complacent" and lacking focus as they lost 2-1 at home to Ostersunds in the Europa League on Thursday.
The Gunners won the first leg in Sweden 3-0 and were expected to cruise in the return fixture at Emirates Stadium.
Goals from Hosam Aiesh and Ken Sema in the space of 70 first-half seconds saw Ostersunds threaten to pull off a huge upset.
And although Sead Kolasinac's strike after the break made it 4-2 on aggregate and settled Arsenal's nerves, Wenger offered a damning verdict of his side's attitude.
"We were not at the races in the first half," he told a news conference.
"We were in trouble because we were complacent and not focused. We were open every time we lost the ball and had no ideas with the ball. That's why we were in trouble.
"In the second half, it was much better. Our energy was high and our domination as consistent. Overall we responded very well. We did the job to qualify. That's what you have to keep from the night and that's it."
Wenger acknowledged his team's convincing win away from home and this weekend's EFL Cup final against Manchester City may have exerted an influence on the mindset of his squad.
"We prepared properly, in a serious way, but you have external circumstances," he said.
"The fact that we won the first leg 3-0, the fact that we have another big game on Sunday, the fact that people subconsciously think they just have to turn up to win the game.
"Football doesn't work like that. We played against a good side and it's what you see in the FA Cup. You can be in trouble every time you're not 100 per cent focused.
"I felt in the first half the whole team was not at the level you expect. It was not easy for the defenders because we lost the ball too early and we didn't' screen well when we lost the ball."
|Fortuna Dusseldorf 2 Borussia Dortmund 1: Bundesliga leaders suffer shock first loss|
|Rivera yet to make a call on sitting Panthers QB Newton|
|Pulisic would thrive in Premier League, but Berhalter expects Dortmund stay|
|Raptors coach Nurse fined by NBA for criticising referees|
|Solari ´loves´ struggling Real Madrid star Isco|
|Mourinho sacked: Pogba, Lukaku, Fred and his other Man United signings rated|
|Mourinho sacked: What does it mean for Manchester United players?|
|Ibrahimovic provides short-term pain, long-term gain for US - Berhalter|
|River Plate 2 Al Ain 2 (aet, 4-5 on penalties): Perez misses decisive spot kick|
|De Bruyne and Aguero back for City, surprise debut for Garcia|
|Uncapped Varun ´panicked a little´ after huge IPL deal|
|Replays scrapped for FA Cup fifth round|
|Pochettino readies big guns for Gunners|
|Ex-Wasps star Wade struggling with NFL transition|
|BCCI rejects ´baseless´ claims over Kohli-Paine ´banter´|
|Ibrahimovic re-signs with LA Galaxy for 2019|
|Mourinho sacked: Solari not worried for Real Madrid job|
|Mourinho sacked: 895 days and more than £700,000 in five-star luxury|
|ES Tunis 1 Guadalajara 1 (6-5 on penalties): Dhaouadi holds nerve to settle ill-tempered affair|
|Murphy lands permanent Tigers role|
|Mourinho sacked: Real Madrid´s Marcelo lauds ´great coach´ after United exit|
|Unadkat, Varun the top buys at IPL auction|
|Emery prepared to give youth a chance in north London derby|
|Tottenham extend Vertonghen contract until 2020|
|Panthers safety Reid receives seventh random drug test of 2018|
|Kovac relishing Klopp challenge in Champions League|
|Bancroft to return, teenager Lamichhane to fly the flag for Nepal in Big Bash|
|Liverpool still have plenty of work to do - Klopp|
|Messi ´never imagined´ his success after winning record fifth Golden Shoe|
|WATCH: Timberwolves´ Gibson tries to block shot with his trainer|
|Mourinho sacked: Klopp praises departed Manchester United boss|
|Mourinho sacked: Jose the best Manchester United manager since Ferguson - Gerrard|
|Mourinho sacked: Ferdinand calls for ´fresh ideas´ at Man United|
|Mourinho sacked: The mystique has gone as United spell ends in divorce|
|´He´s an interest not only for us but for many´ - Zola praises rumoured Chelsea target Wilson|
|Mourinho sacked: Pochettino focused on Spurs amid Manchester United rumours|
|Mendis eyes double-century for departing Samaraweera|
|Mourinho sacked: Zola expects Jose to be in another job ´soon´|
|Mourinho sacked: Five reasons it went wrong at Manchester United|
|Mourinho sacked: Jose´s Manchester United record in Opta stats|
|Mourinho sacked: Pogba, Ronaldo and Jose´s biggest bust-ups|
|Mourinho sacked: Blanc, Solskjaer - the men who could steady the United ship short-term|
|Mourinho sacked: The football world reacts|
|Mourinho sacked: What former United stars said after Liverpool loss|
|Mourinho sacked: Where next for the axed Manchester United boss?|
|UEFA to investigate alleged racist incidents at Vidi-Chelsea|
|Australia unchanged for rest of India series|
|Mourinho sacked: Pogba´s tweet a dig at departing Man United boss?|
|Newton left frustrated by shoulder injury as Panthers lose again|
|Mourinho sacked: Pochettino & Zidane lead potential Man Utd replacements|
|Mourinho sacked: Neville urges Man United to go for Pochettino|
|Boylen pleased to see Bulls react to red rag in Thunder fracas|
|Icardi and Inter ´very far´ apart in contract negotiations|
|Mourinho leaves Manchester United|
|Curry humbled by latest milestone|
|Robertson: ´Unbelievable´ Alisson will bounce back from error|
|Curry scores 15,000th regular-season point in Warriors win|
|Rams star Gurley ´day-to-day´ with knee inflammation|
|Saints poised to clinch NFC top seed after topping Panthers|
|Mathews, Mendis centuries frustrate New Zealand|
|Kohli: Relentless Australia deserved victory|
|Relief for Paine and Australia after ending Test drought|
|Australia level series with dominant win over India|
|Libertadores holders River learn group as CONMEBOL boss calls for end to violence|
|Chargers RB Gordon planning to return against Ravens|
|Kobe Bryant visit motivated Browns´ Jabrill Peppers|
|De Bruyne: Fatigue not behind injury woes|
|´That´s not my concern´ - Broncos coach Joseph on job security|
|Lowry on Leonard´s free agency: I just want him to be happy|
|Yankees give Sabathia $500K bonus despite ejection|