Chelsea winger Willian was on target for Chelsea, and his penalty just before half-time may well have taken the game out of reach for a hard-working Watford side.
Olivier Giroud had already given the Blues the lead at Stamford Bridge, but the Hornets were holding their own until a rash challenge from Etienne Capoue on Christian Pulisic left referee, Kevin Friend, with little choice other than to point to the spot.
Ben Foster filled the Watford goal and tried his best to put the Brazilian off but Willian stroked the ball home with ease.
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