The German champions fell to their first loss since September of last year as their opponents took their chances with clinical efficiency
Robert Lewandowski’s penalty – his 20th Bundesliga goal of the season – and a fine strike from Leon Goretzka put Bayern in control of the Bundesliga clash at Borussia-Park inside 26 minutes.
However, a wayward pass from Benjamin Pavard led to a quick break that finished with Jonas Hofmann scoring, and the Gladbach midfielder was played onside by Niklas Sule as he doubled his tally before half-time after Joshua Kimmich was caught in possession by Lars Stindl.
Sule then gave the ball to Hofmann inside his own half four minutes after the restart and Florian Neuhaus subsequently atoned for conceding the first-half spot-kick with a bizarre handball by netting the winner.
Gladbach consequently became the first team since Cologne in February 2011 to beat Bayern in a Bundesliga game after falling 2-0 down.
“We had hoped for a different ending to this game and expected it, but in the end we were punished. We lost the ball unnecessarily three times and the opposition was brutally effective in finishing those chances,” Flick told a post-match news conference.
“When you ask me how to prevent that, on the one hand you have to keep the mistakes to a minimum, or avoid them, and on the other hand you have to cover your deep positions twice.
“We suffered similar situations on their first two goals. Hofmann went deep from midfield and we moved forward too quickly and opened the centre without covering the deep position, and with the second we should have kept going and covering the positions.
“That shouldn’t happen and it’s not a nice situation to be in, but a defeat, even if it’s Bayern Munich, is part of the game. In the second half the team tried everything to achieve a positive result but unfortunately it didn’t work.”
Manuel Neuer has now conceded in 10 straight Bundesliga games for the first time in his career, with Bayern letting in 16 goals since their last clean sheet against Eintracht Frankfurt on October 24.
Bayern have conceded 24 goals through 15 matches in the top flight this season, the most they have shipped at this point of a Bundesliga campaign since 1981-82.
Flick added: “I’ve said it a few times, we are making too many mistakes. You can’t deny that the team tried to win.
“We had to fight today, we knew it would be a difficult game. Don’t forget [Gladbach] is a team that played in the Champions League against top opposition and prevailed, so we needed this compact team performance and we showed – with the exception of these three situations.
“But of course, we’re not satisfied with the result. We all know we need to show even more concentration in our defensive work in the crucial moments. We have to cover the deep positions and that’s the challenge we have, and we have to improve in the coming weeks.”
Bayern are back in action against 2. Bundesliga side Holstein Kiel in the DFB-Pokal on Wednesday.