Ji Dong-won scored a goal in each half as Augsburg beat Borussia Dortmund 2-1 and gave Bayern Munich a chance to pull level at the top.
Borussia Dortmund's Bundesliga title bid suffered another damaging blow as Ji Dong-won's brace gave struggling Augsburg a 2-1 victory.
Irresistible before the turn of the year, Lucien Favre's side have won only one of their past five top-flight fixtures and Bayern Munich can now go level on points with the leaders by beating Borussia Monchengladbach on Saturday.
A favour from their Bavarian neighbours seemed unlikely, but Ji opened the scoring in the 24th minute and finished superbly after half-time as BVB's defence coughed up costly mistakes.
Augsburg substitute Georg Teigl erred similarly and allowed Paco Alcacer to reduce the arrears but Michel Baum's team held on to move five points clear of the bottom three.
Dortmund started on the front foot and at a high tempo, with the returning Marco Reus unable to squeeze an eighth-minute chance past Augsburg goalkeeper Gregor Kobel.
Jadon Sancho had an effort deflected behind from Achraf Hakimi's cross but Augsburg broke the deadlock – Ji lifting into the top corner from close range after Manuel Akanji blocked his initial shot.
Jacob Bruun Larsen howled in frustration when Kobel kept out his 42nd-minute volley and Dortmund remained behind at the interval.
Things got worse for Favre's men midway through the second half as Hakimi's woeful ball across his own backline allowed Ji to bear down on goal.
He still had plenty to do but some stepovers steadied Dan-Axel Zagadou before the South Korea international floated a wonderful chip into the far corner.
The visitors sent on Alcacer, who drew an excellent reaction stop from Kobel, although the keeper had no chance when Sancho and Mario Gotze worked the opening for the former Barcelona striker from Teigl's slack pass.