The German giants were bested 2-0 at home by Mainz 05.
The relegation threatened team gave themselves a huge chance of staying up.
The defeat is the second in 11 games for Dortmund, who are now ten points behind Bayern Munich in second place.
It was a game that summed up a nearly season for BVB, who had to watch their rivals Bayern clinch the title a day earlier.
Mainz are now five points clear of 16th placed Dusseldorf with two rounds remaining.