Two goals in the first half from Matthew Bates and Adam Johnson set Boro on their way. A late goal from substitute Jonathan Grounds sealed an impressive victory, over a Sunderland side that had beaten Boro 4-0 in a league encounter earlier in the season.
Boro will now play Watford away in the 5th round, after they beat Newcastle 1-0 on Tuesday.
Boro team:
Knight, Burgess, Hines, Bates, Wheater, Kennedy, Owens (Lemaire), Robson (Grounds), Craddock, Walker (Clough), Johnson