The centre-back believes BVB got out of jail on Sunday, while Sebastian Kehl was equally full of praise for Freiburg
Last year's Champions League finalists were sluggish at Signal Iduna Park, but a solitary Sebastian Kehl strike in the second half eventually saw BVB record a 1-0 win.
"I must admit that it was a bit of a lucky win for us," Hummels told Sky Sport.
"We did not create a lot of chances and the referee could have sent off Sokratis."
Kehl, meanwhile, was full of praise for Freiburg as well after BVB's hard-fought win, while he stressed that his goal was not a coincidence.
"Freiburg did a great job. They never let us play our own game and we failed to create any chances of note. It was a difficult match for us.
"I knew that Oliver Baumann stands quite far off his line."
Dortmund sit second in the Bundesliga table following this weekend's results, with the win extending their lead over second-placed Bayer Leverkusen to four points.