Blues hit back to dominate proceedings after the break.BCFC
Despite trailing to a 42nd minute goal, Blues hit back strongly after the break and went on to dominate.
Blues conceded on the counter-attack just before the interval.
And shortly into the second-half Jake Weaver pulled off a brilliant - and vital - save.
From then on, though, Blues took complete control.
Sixteen-year-old Josh Andrews levelled matters up when he slotted the ball smartly past the Watford goalkeeper after a pass was slid through to him in the area.
And the introductions of Olly McCory and Odin Bailey helped provide extra impetus for Blues, who 'overran' Watford in the last 20 minutes.
McCoy was a constant threat down the right hand side and assisted on Blues next two goals, setting up Kyle McFarlane and Bailey to finish and take proceedings away from the Hornets.
Richard Beale, Blues Senior Professional Development Coach, commented: "Second-half we were much better. We were higher up the pitch - we gave them too much space in the first-half - tighter and more aggressive.
"It was a good finish from Josh, and Olly got in constantly a lot down the right.
"After we equalised we overran them, really, we looked fitter and stronger and more dangerous."
Blues: Weaver, Martin, Dacres-Cogley, McGilp, Scarr (Forrest 65), Bajrami, O'Keeffe, Lakin (McCoy 65), Andrews (Bailey 65), McFarlane, Seddon. Subs not used: Anderson, Luyambula.