The young Reds had convincingly seen off Coventry City in round three - scoring three goals in the opening 12 minutes - and wasted no time in proving themselves against North End, who were 4-1 winners over Liverpool back in December to reach this stage.
After another fast start established a four-goal half-time lead, Adam Lawrence's side overcame a second-half resurgence from the visitors to triumph and set up a fifth-round tie between the competition’s two most successful clubs: United, with 11 all-time titles, and Chelsea, the nine-time Youth Cup winners. United will be the home side.
Centre-forward Chido Obi’s clever ball forward seven minutes in allowed James Scanlon to cut it back across goal where, after an initially impressive North End goalline clearance, Jack Fletcher pounced to bundle it home.