Ji Dong-won scored twice against his former club as relegation-threatened Augsburg dealt Borussia Dortmund's Bundesliga title hopes a blow with a 2-1 win on Friday.
Ji, who endured a frustrating half season at Dortmund in 2014, struck in each half to hand Lucien Favre's side only its second defeat of the season and open the door for Bayern Munich to move level on points at Borussia Monchengladbach on Saturday.
Dortmund had two good chances with Marco Reus, returning from injury, having his shot blocked by Augsburg keeper Gregor Kobel, who also saved Manuel Akanji's header.
But a mistake from Dan-Axel Zagadou allowed Andre Hahn to find Ji, who swiped in the rebound after his first effort was blocked by the retreating Akanji.
Kobel then came to Augsburg's rescue before the break when he saved Jacob Bruun Larsen's shot.
Favre brought on Paco Alcacer and Raphael Guerreiro in a bid to find the equalizer with about 25 minutes remaining, but Ji made it 2-0 by chipping the ball over helpless keeper Roman Buerki after a mislaid pass from Achraf Hakimi.
Alcacer was denied by Kobel's brilliant save before breaking his seven-game goalless spell after being set up by Mario Goetze with 10 minutes remaining.
Kobel then made his eighth save against Goetze late as Augsburg moved five points ahead of Stuttgart in the relegation zone.
