The early exchanges were relatively quiet Charliston Benschop had a shot blocked while Berlin’s captain Damir Kreilach headed wide from a corner.
It was the visitors who had the first real chance of the game just under 15 minutes in, Sebastian Polter bore down at Lars Unnerstall from a tight angle but he snatched his effort wide.
Unnerstall then was out quickly and bravely to nick the ball from Max Thiel but was caught by his fellow countryman who received a yellow for the foul.
Finnish striker Joel Pohjanpalo then flashed an effort wide at the other end. That was the last incident of note in a dull first half.
Fortuna started the second half brighter, albeit without really testing the side from East German. Julian Schauerte’s cross caused problems and it eventually came to Michael Liendl but his shot was blocked.
The same combination then saw Liendl’s header brilliantly saved by Hass. Liendl then had another effort just a minute after but Hass again was equal to it.
Substitute Mathis Bolly nearly had an instant pact forcing another good save from Hass, before the Union shot-stopper gathered Pohjanpalo’s shot.
Union had to play the last five minutes with 10 men as Toni Leistner received a second yellow for bringing down Axel Bellinghausen.
The hosts almost immediately capitalised as Bolly cut inside and lashed a shot past Hass with only a couple minutes left, lifting the roof off the Espirit Arena.