The Bluebirds, in their first Premier League game at home, came from behind to score three goals in the second half, prior to City grabbing a second in injury time through Alvaro Negredo.
Aron Gunnarsson cancelled out Edin Dzeko‚Äôs 52nd minute opener on the hour-mark before Campbell headed home twice from corners to give the Welsh side an eventual unassailable lead.
His performance did go unnoticed by Mackay who signed the 25-year old from Sunderland in January.
"I thought Fraizer Campbell gave their whole back four problems today,‚ÄĚ he said.
"He is someone I was delighted to get when we managed to get him in from Sunderland for ¬£600,000. I thought it was an incredible bit of business on our behalf and he hit the ground running.
"He needed to get fit and he needed to get sharper and he needed to regain belief in his own ability and that is what we gave him.
"He worked hard over the summer and I now think I have a player there who has had an England cap and, over the piece, I think could force his way back into that squad if he keeps his head down and keeps working and playing like that against top, top players."