Rudy Gestede struck in the dying seconds to hand the Bluebirds a vital point in their quest for promotion to the Premier League.
Speaking after the game, Mackay said: "To get a goal is relief when you are a goal down with a few minutes to go.
"But it was just reward for the way the team kept fighting to the end. We had a never-say-die attitude to knocking on the door."
Cardiff lead the Championship by four points over second-placed Hull City with 10 games left to play this season.