- Dion Drena Beljo (53')
Union have enjoyed their best ever campaign but with only one win in their last five league games they are fourth in the standings on 56 points, one behind RB Leipzig, 1-0 winners over Freiburg who are fifth on 56.
Union face Freiburg next week in their battle for a top-four finish that leads to next season's Champions League group stage.
The visitors were sharper in the first half, going close with two Kevin Behrens headers but it was Augsburg who broke the deadlock eight minutes after the restart.
Ruben Vargas floated a sumptuous cross into the box and Dion Beljo volleyed home with the hosts' first chance of the second half.
Union had possession and tried to find an equaliser but could not carve out a single clear scoring chance against a solid Augsburg backline.
- Florian Badstübner
|1. FC Heidenheim 1846||14||4||2||8||-9||14|
|1. FC Union Berlin||13||3||1||9||-13||10|
|SV Darmstadt 98||14||2||3||9||-20||9|