Match ends, Borussia Dortmund 0, FC Augsburg 1.
Borussia Dortmund's players went over to their vocal fans at the final whistle after defeat by 10-man Augsburg kept the side rooted to the bottom of the German Bundesliga.
The 2011 and 2012 champions, and last season's runners-up, suffered their 11th league loss in front of 80,000 spectators at the Westfalenstadion.
Roman Weidenfeller and Mats Hummels were seen conversing with spectators.
Raul Bobadilla scored the only goal of the game in the 50th minute.
Augsburg's Christoph Janker was sent off midway through the second half for bringing down Pierre-Emerick Aubameyang.
Dortmund boss Jurgen Klopp said: "We can be accused of anything tonight and it is all justified. Battling also means having the courage to take the right decision. We were missing that tonight."
Hummels said: "If one is in this position after 19 games then it would be unacceptable not to have understanding for the fans' reactions."
Dortmund have 16 points from 19 games, although Jurgen Klopp's men are only two points from safety.
They remain in the Champions League, with a knockout-round match against Juventus coming up on 24 February, but the team make-up is very different to the one that finished runners-up in Europe's premier club competition in the 2012-13 season.
The club have sold key players since winning consecutive league titles, with striker Robert Lewandowski and midfielder Mario Gotze going to arch-rivals Bayern Munich.
And for periods of the season so far, they have been without the likes of World Cup-winning defender Hummels, Marco Reus, Jakub Blaszczykowski, Ilkay Gundogan and Nuri Sahin.
Despite their predicament, Dortmund CEO Hans-Joachim Watzke recently said there was no reason to doubt coach Klopp.
Elsewhere, Hamburg eased their relegation troubles with a 3-0 win over Paderborn, ending a 398-minute league goal drought.
A penalty awarded after just eight seconds - the fastest since timings were introduced in the 2004-05 season - was converted by Rafael van der Vaart to give the northern German side the lead.
Marcell Jansen and Zoltan Schieber scored the other two in a victory that moved Hamburg to 13th spot on 20 points.
- 19GroßkreutzSubstituted forSuboticat 60'minutes
- 11ReusSubstituted forMkhitaryanat 72'minutes
- 23KamplSubstituted forKagawaat 72'minutes
- 16JankerBooked at 64mins
- 25BobadillaSubstituted forDjurdjicat 84'minutes
- 13WernerBooked at 23minsSubstituted forCaiubyat 62'minutes
- 22JiSubstituted forKohrat 65'minutes
- Marco Fritz
- Shots on Target
Second Half ends, Borussia Dortmund 0, FC Augsburg 1.
Attempt saved. Marcel Schmelzer (Borussia Dortmund) header from the centre of the box is saved in the top centre of the goal. Assisted by Henrikh Mkhitaryan with a cross.
Shinji Kagawa (Borussia Dortmund) wins a free kick in the defensive half.
Foul by Nikola Djurdjic (FC Augsburg).
Attempt saved. Ciro Immobile (Borussia Dortmund) header from the left side of the six yard box is saved in the centre of the goal. Assisted by Henrikh Mkhitaryan.
Attempt missed. Sokratis (Borussia Dortmund) header from the centre of the box misses to the left following a corner.
Corner, Borussia Dortmund. Conceded by Alexander Manninger.
Attempt saved. Henrikh Mkhitaryan (Borussia Dortmund) right footed shot from the right side of the box is saved in the top right corner. Assisted by Shinji Kagawa.
Nuri Sahin (Borussia Dortmund) wins a free kick in the defensive half.
Foul by Caiuby (FC Augsburg).
Offside, FC Augsburg. Halil Altintop tries a through ball, but Caiuby is caught offside.
Substitution, FC Augsburg. Nikola Djurdjic replaces Raul Bobadilla.
Attempt saved. Pierre-Emile Höjbjerg (FC Augsburg) right footed shot from outside the box is saved in the centre of the goal.
Foul by Henrikh Mkhitaryan (Borussia Dortmund).
Halil Altintop (FC Augsburg) wins a free kick in the attacking half.
Foul by Caiuby (FC Augsburg).
Sokratis (Borussia Dortmund) wins a free kick in the defensive half.
Raul Bobadilla (FC Augsburg) wins a free kick in the defensive half.
Foul by Shinji Kagawa (Borussia Dortmund).