Middlesbrough claimed bragging rights in the Wear-Tees derby with their biggest away victory over Sunderland.
Second-half goals from Leeds United loanee Sam Greenwood, Matt Crooks, Isaiah Jones and Marcus Forss made it four successive wins for Boro as they continued their recovery from a poor start to the season.
The turning point came in first-half injury time when Black Cats midfielder Dan Neil was sent off for a second yellow card offence.
The home team could not cope without him as they slipped to a fourth loss of the season, although they remain in the top six.