Bayern Munich squandered a two goal half-time lead in Cologne to lose further ground at the top of the Bundesliga.
The champions were seemingly cruising at 2-0 going into the break, despite being without flu-ridden Dutch winger Arjen Robben.
Bundesliga top scorer Mario Gomez broke the deadlock on 22 minutes, slotting home his 16th goal of the season. Turkish international Hamit Altintop doubled the advantage just before the interval when he fired home from a tight angle.
A second-half collapse of Rome proportions (where the Reds also threw away a two goal Champions League advantage back in November) ensued. From a position of complete dominance, the Double winners fell apart against 3rd bottom side Cologne.
Bayern's soft underbelly was repeatedly exposed. German international Holger Badstuber struggled alongside Ukrainian Anatoliy Tymoshchuk at the heart of the defence. Badstuber was lucky to stay on the pitch after a professional foul in the first half. Former captain Mark van Bommel's gritty presence and dominant leadership was also badly missed in midfield.
Goals from Christian Clemens (55 mins.) and a brace from Slovenian striker Milivoje Novakovic (62, 73 mins.) earned the Billy Goats an amazing comeback victory.
"We lost due to our own stupidity,'' commented a frustrated Thomas Müller.
Champions-elect Borussia Dortmund could only draw 0-0 in the "Ruhr Derby" against Schalke 04, but still managed to increase their advantage at the top of the table. Chairman Karl-Heinz Rummenigge remarked, "Dortmund must be laughing themselves silly.'' Bayern now trail Dortmund by 15 points with 13 games of the season remaining.
"I am angry, disappointed and astounded,'' fumed Coach Louis van Gaal. The Dutchman will find the heat being increased in the coming weeks, especially with the crunch showdown against European champions Inter Milan on the horizon.
Bayern slip down to 5th place and outside of the Champions League qualification spots.