The Blancos snatched a hard-fought win over the UCL debutants.
Real Madrid defeated Union Berlin 1-0 in their Champions League match on Wednesday. Jude Bellingham scored again as the Blancos started the new UCL campaign with a victory.
Real Madrid established their dominance early on but struggled to make clear-cut chances before the break. The hosts maintained their defensive integrity as they spent most of the first period in their own half.
Real Madrid doubled down on their pressure as soon as the second half started, coming close to scoring the opener several times. Rodrygo and Joselu hit the posts as visitors looked set to escape Santiago Bernabeu with a point.
However, Bellingham rescued Real Madrid again as he smashed a deflected ball into the back of the net in the 94th minute. The victory sends the Blancos to the top of the Group C standings. Elsewhere in the group, Napoli take on Braga later tonight.
Real Madrid: Kepa (7); Lucas Vázquez (8), Rüdiger (7), Alaba (7), Nacho (7); Modric (8), Tchouameni (7), Camavinga (7); Bellingham (8); Joselu (7), Rodrygo (6).
Bench: Kroos (7), Valverde (7), Garcia (6), Diaz (6).
Union Berlin: Ronnow (8); Gosens (6), D. Leite (7), Bonucci (7), Doekhi (7), Juranovic (6); Král (6), Tousart (5), Laïdouni (5); Becker (6), Behrens (6).
Bench: Aaronson (6), Vollan (5), Jeckel (6), Fofana (6), Kemlein (5).