Watford strengthened their grip on second place in the Championship as they scored four goals against relegation-threatened Rotherham.
Francisco Sierralta gave the Hornets the lead with an early header, before Ismaila Sarr's instinctive finish and Ken Sema's volley put them on course for a fourth successive win before half-time.
Rotherham saw a Michael Smith penalty saved by Daniel Bachmann early in the second half before Freddie Ladapo gave the hosts hope of a comeback with a superb solo run and strike.
But that proved to be short-lived as substitute Dan Gosling netted Watford's fourth from the restart as he swept in the rebound after Andre Gray's shot was saved by Jamal Blackman.