"Arjen played it deep, I didn't really have time to see where to put it, I just hit it and had a bit of luck that it went in", said the Germany star. But Bayern regained the lead seven minutes later with a crafty effort from Mueller who got to the byline, saw that Faehrmann was expecting him to pull the ball back and threaded his shot between the goalkeeper and the near post.
Plenty has changed since he last started a game for Dortmund.
Eight months ago the 28-year-old partnered Ousmane Dembele and Pierre-Emerick Aubameyang up front. As promised, the Belgian striker celebrated with a somersault.
Dortmund's injury-prone Germany winger Marco Reus returned after 259 days sidelined by a torn knee ligament. The away side looked to play on the counter attack at it was them who had the best opportunity of a first half with very little chances.
A boring match was lit up by Dortmund's second in the dying stages when Germany's World Cup victor Mario Goetze netted with a goal after coming off the bench.
Eintracht Frankfurt defeated bottom club Cologne 4-2 at home to move to fourth, the last place for a Champions League playoff.
Hannover ended Freiburg's nine-game unbeaten run with a 2-1 win at home to consolidate its midtable spot, level on points with Hoffenheim and Augsburg.
Bayer Leverkusen dropped to fifth after a shock 2-0 defeat at home to Hertha Berlin as Valentino Lazaro and Ivory Coast veteran Salomon Kalou scored.