Mats Hummels said Germany's tactical approach was wrong after the World Cup holders lost the opening game of their title defence 1-0 to Mexico.
Hirving Lozano struck the only goal of the Group F clash, but Mexico wasted numerous chances on the break to record an even larger margin of victory.
Germany, meanwhile, had 26 shots without causing Guillermo Ochoa too many problems, although the Mexico goalkeeper made nine saves in keeping a memorable clean sheet.
Hummels felt Germany did not heed the warning of their final warm-up friendly against Saudi Arabia that ended in a tight 2-1 win, their only success in seven matches since the end of the World Cup qualifying campaign last year.
"It's pretty simple. We played like we did against Saudi Arabia, but against a better opponent," Hummels said to ZDF.
"We talked about a few things, such as not losing possession and protection, which unfortunately we did not put into action today.
"Mexico deserved the game because we made it too easy for them, knowing we should not have allowed that to happen.
"If seven or eight players play offensively, then it's clear that the offensive force is greater than the defensive stability. That's what I often say internally.
"Our stability is not good, you have to say - often only Jerome [Boateng] and I were at the back, so they mercilessly attacked us."
Germany will still expect to progress - they face Sweden and South Korea in their remaining matches - but Hummels told his team-mates to buck up their ideas.
"A wake-up call is too late, we now have to win two games, otherwise the World Cup is over," Hummels said. "We actually had the wake-up call against Saudi Arabia."
1 - Opening game at the World Cup for reigning champions in the 21st century:— OptaJean (@OptaJean) June 17, 2018
2002 France 0-1
2006 Brasil 1-0
2010 Italy 1-1
2014 Spain 1-5
2018 Germany 0-1
Pressure. #GERMEX #WorldCup pic.twitter.com/8g3kXZHSwA
Real Madrid midfielder Toni Kroos joined Hummels in demanding an improved performance when Germany take on South Korea on Wednesday in Kazan.
"I think we did not find any solutions in the first half," Kroos said.
"Mexico were clever, we did better in the second half and Mexico got tired.
"We're under pressure now, without question, we have to get six points from the two games, if possible."
13 de noviembre 2018
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|Watson among four signing new Bath deals|
|Susanna Dinnage to replace Scudamore as Premier League chief executive|
|Murray commits to Brighton until 2020|
|Rooney rejected chance of pre-World Cup farewell|
|Impressive Anderson thrashes Nishikori|
|Ozil´s Germany absence a ´pity´, says Sane|
|Rooney: I´ll finish my career in the US|
|McIlroy unsure of 2019 European Tour membership|
|Australian Open dismisses concerns of Federer scheduling bias|
|Hue Jackson joins Bengals staff as ´special assistant´|
|Real Madrid confirm Reguilon injury|
|Higuain handed two-match ban for Juve meltdown|
|Kruis ruled out for England as Jones calls up uncapped quartet|
|A year on from Italy failure, Ventura leaves Chievo after four games|
|Bairstow misses out as unchanged England promote Stokes|
|Recalled Alba denies Luis Enrique bust-up|
|´Unhappy´ Christensen won´t push for Chelsea exit|
|Nadal to make Abu Dhabi comeback in December|
|Taijul helps Bangladesh tighten their grip despite Taylor ton|
|Neymar joining Real Madrid wouldn´t hurt Iniesta|
|It´s just team spirit - Livingston not worried by Durant-Green exchange|
|Trippier out of England squad with groin injury|
|Ex-Sri Lanka international Lokuhettige charged by ICC|
|Former England and Chelsea star Joe Cole retires|
|Nets offer support to LeVert following serious leg injury|
|Panenka proud Sergio Ramos imitates his penalties|
|Liverpool´s Alisson seeks patience to reach potential|
|Anthony Davis leads Pelicans, Clippers hold off Warriors in OT|
|Lindelof rues international break for Man Utd|
|Shaqiri confident in more goals for Liverpool|
|Giants too good for 49ers in crunch time|
|Southgate named honorary Yorkshireman|
|Nicky Butt: Manchester United are low on confidence|
|Criticism of Barcelona star Dembele is overblown - agent|
|Thibodeau discusses Butler trade: We thought this was the best deal for us|
|Acuna, Ohtani win rookie of the year awards|
|LeBron James on Lakers’ early season struggles: ‘I almost cracked’|
|Welbeck has successful second operation on broken ankle|
|UEFA warns FFP cases can be reopened based on ´new information´|
12 de noviembre 2018
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|WATCH: Rooney looking sharp in England training return|
|Mbappe: Money in football is truly indecent|
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|Ibrahimovic beats Rooney to MLS Newcomer award|
|Rams WR Kupp out for season with torn ACL|
|Sturridge denies ever gambling on football following FA charge|
|Koeman understands De Ligt´s Eredivisie frustrations|
|Jimmy Butler trade: 76ers acquire Timberwolves star in blockbuster deal|
|´Improve your attitude´ - Deschamps issues Dembele warning|
|Sturridge charged with misconduct over alleged breach of betting rules|
|Saints sign Marshall following Bryant injury|
|Mendy suffers knee injury, leaves France squad with Lacazette|
|Zverev beats Cilic in error-strewn London battle|
|Rafinha replaces injured Casemiro in Brazil squad|
|´One-dimensional´ Australia batsmen need work before World Cup - Finch|
|Mancini keen to work with ´incredibly gifted´ Tonali|
|Italian manager of the year Allegri targets long Juve stay|
|Injured Lee departs as Wales prepare squad for Tonga|
|Conte content to wait until June for coaching return|
|Etzebeth set to return, Whiteley a doubt for Scotland Test|
|In-form Verstappen does not need distractions from 2019 challenge|