Schalke coach Huub Stevens has slammed his side for their "schoolboy'' performance in the Ruhr derby.
They were beaten 2-0 on Saturday, but they were fortunate not to lose by an even greater margin as the defending champions confirmed their return to form in emphatic style.
And Stevens could find no defence for his players.
"If you want to survive here, you have got to be at your best and we know that,'' he told Sky television. "There were far too many of our players who were on the level they usually play at.
"In the first half, there were phases when my team of adults looked like a team of schoolboys and that is not on. I hope that this is a good lesson to the lads.''
Stevens spoke of a "huge disappointment'' at his side's performance, but he paid tribute to his opponents.
"Of course it had something to do with who we were up against and they are further on in their development than we are,'' he said. "Nevertheless, we should not be just surrendering like we did in the first half. That was too little.''
While Stevens struggled to find any positives in his side's performance, his Dortmund counterpart Jurgen Klopp could not find anything negative to say about his side.
"It was simply a great game from start to finish,'' he said. "We fully deserved to win.''