The former Bayern Munich man was impressed with BVB being able to put the euphoria from the victory over Real Madrid in midweek behind them and claim another win on Saturday
Jurgen Klopp's men were forced to play in difficult weather in Breisgau with snow making conditions treacherous.
Nevertheless, Hummels believed BVB showed character to recover from a poor first half and grab a vital win courtesy of goals from Neven Subotic and Mario Gotze after the break.
"It's undoubtedly an important victory. We had to switch from the game against Real Madrid, because of how the table is now. We have proven that we can rise to the challenge," the defender is quoted as saying by Ruhr Nachrichten.
"We are a good team, but now we need to maintain the right attitude. The first 45 minutes were not good, but we knew at the break that it would get better."
"It was not a good game of football, because that was not possible on this ground. But it's true that Freiburg adapted to the conditions better than us in the first half."
Dortmund find themselves nine points off league leaders Bayern Munich, who face Bayer Leverkusen on Sunday.