Augsburg stunned Bundesliga leaders Bayern Munich 2-1 on Saturday to end a 27-match unbeaten league run for their Bavarian rivals dating back to March.
Hiroki Ito's opener gave the defending champions an early lead, but Augsburg fought back with two goals in six second-half minutes from Arthur Chaves and Han-Noah Massengo.
Second-placed Borussia Dortmund could cut the gap to Bayern to eight points with a victory at Union Berlin later on Saturday.
"We have to accept it – it wasn't undeserved. It wasn't like Augsburg dominated us, but a win for us would not have been deserved either," Bayern's Joshua Kimmich told Sky Germany:
"Augsburg were more aggressive towards the end. It wasn't the top level we wanted to deliver, but what's most crucial is how we react to it."
Bayern have been unstoppable this season. They had recorded the best opening half of a season in Bundesliga history and dropped just four of a possible 54 points in 18 games.
The hosts looked set for a routine victory when Ito headed in a Michael Olise corner after 23 minutes.
Unfancied Augsburg last won a match in early December but fought back when Chaves made the most of a mistake from Bayern's back-up goalkeeper Jonas Urbig to level with 76 minutes gone.
MEMORABLE VICTORY
Massengo then finished off a superb team move to put Augsburg in front and on track for their first win in Munich since 2015.
Olise hit the post deep in stoppage time, but Augsburg held on for a memorable victory.
Over 400 kilometres away, Bayer Leverkusen fans celebrated Bayern's loss, chanting "the only unbeaten champion," celebrating as they remained the only undefeated Bundesliga title winners, having done so in 2023-24.
Leverkusen beat Werder Bremen 1-0, with former Real Madrid defender Lucas Vazquez scoring the only goal to snap a three-game losing streak, and climb to sixth in the table.
Elsewhere, surprising Hoffenheim tightened their grip on a top-four spot with a come-from-behind 3-1 win at struggling Eintracht Frankfurt.
Frankfurt, who sacked coach Dino Toppmoeller last Sunday, took the lead through Arnaud Kalimuendo, but Hoffenheim turned the game around with three goals in 13 second-half minutes.
Max Moerstedt and Ozan Kabak scored before Aurele Amenda put through his own net as Hoffenheim, relegation battlers last season, solidified their hold on third spot, three points behind second-placed Dortmund.
RB Leipzig cruised past Heidenheim 3-0 to move up to fourth, thanks to goals from Ridle Baku, Antonio Nusa and captain David Raum.
Mainz beat Wolfsburg 3-1 to continue their recent resurgence. Rock-bottom at Christmas, Mainz have claimed nine points from their past six matches to climb into the relegation playoff spot.