Tony Mowbray’s side were fortunate to still be level at half-time after Anthony Patterson saved Joe Ralls’ penalty.
Cardiff took the lead four minutes after the restart, though, as Mark Harris converted Mahlon Romeo’s low cross.
The hosts did apply some late pressure but couldn’t force an equaliser.
Our Sunderland writer Phil Smith has dished out his player ratings from the Stadium of Light:
9. Amad - 5
Was definitely Sunderland’s most dangerous player throughout the second half but couldn’t quite find the end product. A frustrating afternoon. 5 Photo: Frank Reid
10. Jack Clarke - 5
Came close to scoring in the opening minutes of the game but struggled to maintain an attacking threat after that. Sunderland never really got him on the ball and he was short of his best when they did. 5 Photo: Martin Swinney
11. Ellis Simms - 5
Went closest with his final touch of the game, nodding a cross onto the roof of the net. Wasn’t at his best as he builds up to match fitness, couldn’t really hold it up and spurned a couple of good chances to play team-mates in. 5 Photo: Martin Swinney
12. Alex Pritchard (sub) - 6
Did get on the ball and added some composure, but Cardiff were able to defend their lead comfortably. 6 Photo: Frank Reid