After an even first half, Black Cats midfielder Dan Neil was shown a second yellow card for dissent as the hosts were reduced to 10 men.
Middlesbrough then took full control after their interval as Sam Greenwood and Matt Crooks both scored in the space of three minutes.
The visitors then added a third when Isaiah Jones broke down the right and converted with a calm finish, before a last-minute goal from Marcus Forss.
1. Sunderland fans
Sunderland were beaten 4-0 by Middlesbrough at the Stadium of Light – and our cameras were at the game. Photo: Frank Reid
2. Sunderland fans
Sunderland were beaten 4-0 by Middlesbrough at the Stadium of Light – and our cameras were at the game. Photo: Frank Reid
3. Sunderland fans
Sunderland were beaten 4-0 by Middlesbrough at the Stadium of Light – and our cameras were at the game. Photo: Frank Reid
4. Sunderland fans
Sunderland were beaten 4-0 by Middlesbrough at the Stadium of Light – and our cameras were at the game. Photo: Frank Reid