For the second time in this cup campaign the Under 18s scored four goals without reply and as at Nottingham Forest in round four, this win and the margin of victory was thoroughly merited.
The goals came from Aliu 'Kaby' Djalo, Marko Mitrovic (his fourth of the cup run), Jeffrey Bruma and Josh McEachran.
Blues coach Dermot Drummy told the club's website: "It was a great team performance. You have to remember Watford went to Anfield and won 1-0 and are a good side but when we moved the ball quickly we were effective.
"There was a period when it was 3-0 when I thought we tried to play schoolboy football but we rectified that and we ran out worthy winners."