Despite taking an early two-goal lead, Chelsea were pegged back and taken to extra-time.
An early goal came through Harry Vale.
Chelsea doubled our lead with a piercing counter-attack which allowed Jude Soonsup-Bell to round the keeper and unselfishly lay it off for Malik Mothersille to tap in.
Watford did create some half-chances but their goal came through a mistake by Prince Adegoke as his attempted dribble proved costly with the hosts' striker Emmanuel Adeyemo pouncing and scoring.
After the break, Chelsea conceded an equaliser which drew the Hornets level. A great cut-back into the box found Adrian Blake who rifled into the top corner.
2-2 was how it ended in normal time, with extra-time the order of the day. Substitute Tudor Mendel-Idowu had a great chance to give Chelsea the lead but his shot was inches over the bar.
With penalties looming, Chelsea did find a winning goal on the stroke of half-time in extra-time as the impressive Vale swept home after a blocked Leo Castledine shot.
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