Union Berlin's fairytale run at the top of the Bundesliga continued on Sunday after a howler from Borussia Dortmund goalkeeper Gregor Kobel helped them to a stunning 2-0 win over Edin Terzic's side.
Two first-half goals from Janik Haberer put Union into dreamland as they extended their five-week run at the top of the table and inflicted a fourth defeat of the season on Dortmund.
The visitors got off to a nightmare start after Kobel handed Union the opener on a silver platter.
As he stepped up to receive a routine backpass from Raphael Guerreiro, Kobel slipped on the grass in his own penalty area, allowing Haberer to tap the ball into the empty net.
Haberer doubled the lead shortly afterwards, smashing the ball into the bottom corner after Union had danced through the lethargic Dortmund back line.
Terzic brought on three attacking players at halftime to try and force a fightback, but it was Union who continued to have the better chances.
Timo Baumgartl forced a sharp save from Kobel early in the second half and only a desperate challenge from former Union defender Nico Schlotterbeck denied Andras Schaefer a few minutes later.
Dortmund pushed hard in the final 15 minutes, forcing three brilliant saves from Union keeper Frederik Ronnow.
In Sunday's early game, former Dortmund striker Steffen Tigges struck twice to lead Cologne to a 3-2 win over Augsburg.
Augsburg took the lead with their first chance of the game, Florian Niederlechner squeezing the ball past goalkeeper Marvin Schwaebe after a long ball into the box.
Tigges levelled the scores with a brilliant first-time finish just after halftime, and was then involved in the build-up to Cologne's second, as Denis Huseinbasic put the home side ahead.
Augsburg remained brutally efficient when they did get forward, and Daniel Caligiuri swept in an equaliser just a few minutes later.
Yet Tigges remained a thorn in the visitors' side until the death, prodding home the winner with just nine minutes to play.