Under-fire Borussia Dortmund coach Peter Bosz admitted Saturday's 4-4 draw at home to Schalke "hurt", after his side surrendered a four-goal lead to their derby rivals in the Bundesliga.
Dortmund were on course for a thumping win after racing into a 4-0 lead with only 25 minutes gone, but the hosts collapsed in the second half after Pierre-Emerick Aubameyang was sent off for a second yellow card.
After Aubameyang opened the scoring, an own goal by Schalke midfielder Benjamin Stambouli, plus a Mario Goetze header and volley from Raphael Guerreiro gave Dortmund a commanding lead to leave Schalke stunned.
But the second half was a totally different story.
Guido Burgstaller and Amine Harit clawed goals back for Schalke before the hosts had Aubameyang sent off in the 72nd minute for a second yellow card.
Borussia's collapse was completed when Daniel Caligiuri blasted home to make it 4-3 late on before Naldo's late header delighted travelling fans and stunned the hosts as Schalke came back from the dead.
"It's hard because you can only feel disappointment in your body," Bosz told Sky, as the draw left Dortmund winless in their last six league games.
"That shouldn't have happened when you play so well and put in a convincing display with a strong performance.
"In the second half we should have scored a fifth goal through Aubameyang, but it shouldn't happen that you are pulled back to 4-4, even with the red card.
"We stopped playing football and didn't use our room."
Bosz said Aubameyang deserved his red card after barging goal-scorer Harit off the ball.
"That shouldn't have happened, he wanted to help, but that was too aggressive, especially as he already had a yellow," fumed Bosz.
Dortmund finished the game with no forwards after Bosz took off winger Andriy Yarmolenko, Goetze came off injured and Aubameyang was dismissed.
Dortmund's CEO Hans-Joachim Watzke and director of sport Michael Zorc have backed Bosz, but each passing week without a win further undermines his position.
Dortmund's 2-1 home defeat by Tottenham Hotspur on Tuesday ended their hopes of reaching the last 16 of the Champions League, but the team are backing their boss, despite being booed off by their own fans.
"The fact is we stand behind the coach, it is clear that there will be discussions out of this and everything will be criticised," said midfielder Nuri Sahin.
"The fact that the fans whistled us, which is completely understandable.
"However, if we had won the game, all the talk would be about the tactical genius of our coach. We took Schalke apart in the first half."
The result leaves Schalke third in the table, three points ahead of fifth-placed Dortmund, and protects the Royal Blues' unbeaten run, having now gone eight games without defeat.
"It was a very difficult phase at the start for us, in which Dortmund overran us and they seemed to score from every shot at goal," said Schalke coach Domenico Tedesco.
In a bid to avert a debacle, Tedesco brought on midfielders Leon Goretzka and 20-year-old Harit on 34 minutes, which turned the tide.
"We had our backs to the wall and we needed a lot of changes," said the Schalke coach.
"Our goal was just to win the second half, realistically you don't play for a 4-4 draw, but after we got back to 4-3, we all believed in it.
"Schalke has proven that they have the mentality and the character to be able to offer a spectacle.
"That was a big step in the right direction and is the reason why we're happy."