Cardiff City moved four points clear of the Championship relegation zone as Mark Harris' goal gave them a 1-0 win at the Stadium of Light.
Cardiff might have led at the break but Joe Ralls' penalty was saved by Anthony Patterson, with the Bluebirds missing a succession of first-half opportunities.
Sunderland improved after Cardiff's goal but never really looked like forcing an equaliser.
The victory lifts Cardiff up to 14th in the Championship, with Sunderland 13th.
Cardiff's victory meant they have won three consecutive league matches against Sunderland for the first time since December 1959, with the success merited after a good performance, especially before the interval.