Commons went down easily in the area under slight pressure from Mensing in the Hoops' 3-0 Scottish Cup win on Sunday before converting the ensuing spot-kick just over ten minutes into the second half.
The goal opened the scoring for the reigning Scottish champions and Mensing felt the decision made to award Commons a penalty was incorrect.
"I don't think it was a penalty. Commons was doing it during the game. He is a clever player," Mensing said.
"The referee Steven McLean got that one wrong.
"Commons went down too easily and I know that for a fact. I'm really disappointed with it. Commons didn't say much to me and I don't think he could justify it.
"He was doing it all over the park, but what can you do? You really expect it now. You just hope the officials see it and don't give it.
"That was the pivotal moment. The longer it was at 0-0 we always had a chance.
"The ref said he felt it was a definite penalty.
"I would argue until I'm blue in the face it wasn't, but it's not going to change anything."