Birmingham City boss Wayne Rooney's winless start to his Blues reign reached a new low on Wearside as the visitors suffered a fourth loss in the five games since he took charge.
Tony Mowbray's side proved too strong as Birmingham were soundly punished for poor defending.
Blues old boy Jobe Bellingham, meeting the side he left in the summer for the first time, nonchalantly put Sunderland ahead on 17 minutes with his first goal in three months.
Koji Miyoshi levelled nicely for Blues on the half hour, but Sunderland went on to win it with two second-half strikes.