Hansi Flick rued a timid Germany performance as Belgium "took full advantage" to seize an unassailable early lead in Tuesday's 3-2 friendly triumph in Cologne.
Yannick Carrasco and Romelu Lukaku fired Domenico Tedesco's new-look Belgium into a 2-0 lead inside nine minutes at RheinEnergieStadion.
A Niclas Fullkrug penalty, his sixth goal in as many international appearances, brought Flick's side back into it before Kevin De Bruyne – who created Belgium's first two goals – put the game out of reach.
Serge Gnabry managed a late consolation but Flick acknowledged there was no way back after Tedesco's visitors punished a woeful start to earn Belgium's first win against Germany since 1954.
"We were too cautious, too passive and weren't able to put our opponents under pressure, and Belgium took full advantage," Flick said on RTL.
"Our passion brought us back into contention, but it wasn't quite enough to get a result."
While a late fightback offered Flick reason for hope, Germany must improve and make use of their international friendlies, given they have automatically qualified for Euro 2024 as a host nation.
Their cause was not helped by Leon Goretzka limping off with an ankle injury in the first half, raising fears the midfielder will not feature in Bayern Munich's crucial Bundesliga meeting with Borussia Dortmund.
Just a point separates Bundesliga leaders Dortmund and Bayern ahead of Saturday's Klassiker at Allianz Arena, with Thomas Tuchel set to take charge of the reigning champions for the first time.
The former Chelsea coach's appointment came after the dismissal of Julian Nagelsmann last week, but Tuchel may be boosted by the injury update Goretzka provided after the match.
Bayern star Goretzka, who appeared in an upbeat mood, told reporters: "I've twisted my ankle. It shouldn't last until Saturday."
