Union thought they had raced into a fourth-minute lead when Robin Gosens smashed home from close range, only for VAR to rule the strike out for an offside earlier in the move.
A breathless half then followed, with Sheraldo Becker missing a pair of chances before making it third time lucky by rounding off a rapid counter-attack with a low and powerful shot under Matheus, after running onto Alex Kral’s through ball.
Bruma was then denied by Frederik Ronnow at the other end, before Becker grabbed his second, emphatically curling home from the edge of the area.
Braga would pull one back before the break though, as Sikou Niakate converted from close range after the rebound from Ricardo Horta’s effort landed in his path.
That opened the door for a second-half revival, and the comeback was completed just minutes after the restart when Bruma netted an absolute screamer, bending the ball into the top corner from 25 yards after a Horta knockdown from a corner.
Horta himself then had a fizzing effort saved, as Braga looked to take the lead for the first time.
Still being roared on by a raucous crowd in their first-ever home Champions League clash, Union were by no means done either, as Kevin Volland’s well-struck half-volley was caught by Matheus.
And shortly afterwards, Becker came close to restoring the lead for Urs Fischer’s side, but could only find the side netting from a tight angle.
Not long after that frustrating miss, substitute Brenden Aaronson should have made it 3-2 when he missed a free header from close range in the dying minutes.
Almost poetically, he was made to pay for that when Castro struck a low drive into the bottom corner from 20 yards, ensuring Union Berlin have now lost six successive games across all competitions after conceding beyond the 90’ mark for a second successive Champions League matchday.
As for Braga, this was the perfect riposte for a loss to Napoli on matchday one, and a huge statement of intent moving forward.
Flashscore Man of the Match: Bruma (Braga)
Real Sociedad claim three points in Salzburg
In the other early Champions League fixture of the night, Real Sociedad won 2-0 away at Salzburg to take themselves to the top of Group D at least temporarily.
