The tie finished 0-0, with midfielder Bellingham catching the eye as a second-half substitute.
It marked Bellingham's first competitive appearance for Dortmund since his move from Sunderland earlier this month. Also appearing was on-loan Chelsea midfielder Carney Chukwuemeka for BVB.
Afterwards, BVB coach Niko Kovac said: "Fluminense is a top team. We weren’t as aggressive as I expected in the first half. It was hard for us, we had to run a lot.
"Overall, it was a lucky point for us. But a draw against a Brazilian team is always a good start, and now we have to win the next games."
Featuring for Flu in defence was Thiago Silva who said afterwards: "For myself, I think I played well. The team did as well. It was very important to compete (well) today against Dortmund. They are very strong. Their back five is not easy to penetrate. I’m very happy for the team today. Now we need to recover well for the next game."