Unnerstall had been made a scapegoat by certain sections of the Schalke faithful for recent results and Stevens protected him from further abuse by leaving him on the bench and counting on the experience of 33-year-old Hildebrand.
"There have been lots of whistles against Lars recently and when a young goalkeeper gets jeered, then the coach has got to do something," Stevens said.
"It's not as if he's made that many mistakes anyway. We wanted to get a bit more calm in the stadium. Unfortunately that didn't happen because there were whistles aimed at the whole team anyway.
"I would like to emphasise that it's only a small minority of the fans and I hope that was clear."
Former Germany goalkeeper Hildebrand was not completely fault-free, especially for Gladbach's goal, but he was delighted to end nearly four months on the sidelines.
"I am delighted to be back between the sticks - that's my second home," he said.
"Sometimes you save them, sometimes you don't. It was a toe-poker and I got a touch to it."