New Watford manager Slaven Bilic got off to a sensational winning start as his rampant Hornets side scored four goals at Stoke.
Ismaila Sarr earned Watford a deserved half-time lead when he evaded the linesman's flag to controversially head home from 12 yards.
But there was no doubt about any of the other Watford goals as the visitors snuffed out any hopes of a second-half rally when they scored three times in the final half-hour.
Ken Sema got a close-range second on 64 minutes, before Keinan Davis and Vakoun Bayo wrapped up their biggest win in 18 months.