- Sheraldo Becker (30', 37')
- Sikou Niakate (41')
- Bruma (51')
- André Castro (90'+4')
Union have now lost their last six matches in all competitions, with their last win dating back to August. They also conceded a late goal in their opening group-stage loss at Real Madrid.
Suriname international Sheraldo Becker scored twice in seven minutes in a rampant first half with the hosts in complete control in their first ever Champions League home game, played in city rivals Hertha Berlin's bigger arena, the Olympic stadium.
The Germans wasted several more scoring chances before the Portuguese pulled a goal back four minutes before the break through Sikou Niakate, who made amends for scoring an own goal in last month's group opener against Napoli.
The visitors drew level with a sensational curled shot from Bruma from 20 metres out in the 51st.
Becker repeatedly went close to a hat-trick in the second half and Union substitute Brenden Aaronson narrowly missed the target with an 86th-minute header but Castro thundered in a low shot from outside the box to snatch the three points.
- Srdjan Jovanovic