The result saw their lead at the top of the Championship cut to five points, but Mackay feels that his side should have been awarded a penalty when Craig Bellamy was felled in the second period.
"I spoke to the fourth official about it and asked him the ruling. Their player was inside the area and Craig Bellamy was on the line on his way in, and the ruling is that is a penalty," he told reporters.
"On the line is inside so unfortunately the referee got it wrong. I thought he had a good game tonight, but it was a key decision and he got it wrong."