Nine-man Borussia Dortmund collapsed to a nightmare 4-2 Revierderby defeat against bitter rivals Schalke, leaving Bayern Munich as strong favourites to win a seventh consecutive Bundesliga title. 

Lucien Favre's side looked set to keep their bid for glory on track when Jadon Sancho brilliantly created Mario Gotze's early goal but Daniel Caligiuri converted an 18th-minute penalty. 

Salif Sane gave Schalke the lead before the half hour and Caligiuri scored a magnificent free-kick in between red cards for Marco Reus and Marius Wolf as Dortmund imploded at a remarkable rate. 

Axel Witsel pulled one back five minutes from time but Breel Embolo lashed another fine finish into the bottom corner, sparking more delirious celebrations from the travelling Schalke contingent.

Bayern will go four points clear at the summit with three games to play if they beat struggling Nurnberg on Sunday.