Mackay insisted that the 25-year-old is still working his way back after a lack of game time, but enthused about his overall performance for the side.
"I am delighted for him, you could see the quality there," Mackay told reporters after the game. "You could see the intelligence, the strength and the link-up play. And for him to get the two goals is obviously really pleasing for him.
"More than anything I am delighted about the lack of ego about the boy and the way he has thrown himself in to everything we do here. He has bought into it and he has grasped it.
"I felt it was time to start him and it is about bleeding him in gently. He has not played a lot of football in the last few months and we have to treat him properly as he builds up to match fitness."
Campbell joined Cardiff from Sunderland in the January transfer window for a reported fee of £650,000.