Borussia Dortmund captain Marco Reus apologised for letting his team down with a red card in the chastening 4-2 derby defeat at home to Schalke.
Dortmund took an early lead through Mario Gotze but their afternoon and Bundesliga title hopes unravelled thereafter, with Daniel Caligiuri equalising from the penalty spot and Salif Sane giving the visitors a half-time lead at Signal Iduna Park.
There was no way back after Reus received his marching orders for a lunge on Suat Serdar – Caligiuri scoring spectacularly from the resulting free-kick.
Marius Wolf foolishly replicated Reus' tackle on Serdar and was sent off five minutes later as Dortmund's composure deserted them.
Breel Embolo completed a famous win for Schalke after Axel Witsel briefly reduced the arrears for the nine men.
Reus led extended protests against referee Felix Zwayer after his dismissal but, on reflection, he felt he could have no complaints.
"It was a clear red card. I was late," he told Sport1.
"Anyone who knows me knows that I did not want to hurt him. I am sorry to the team."
Bayern Munich will go four points clear of Dortmund at the Bundesliga summit if they win at struggling Nurnberg on Sunday and BVB head coach Lucien Favre declared his team's title hopes to be over after the derby.