Marvin Sordell scored twice for Watford against 10-man Doncaster to extend his team's unbeaten run to eight games.
The England Under-21 international opened the scoring before Billy Sharp equalised, but Sordell's glancing header restored Watford's lead.
Further goals from John Eustace and on-loan Michael Kightly ensured the win for Sean Dyche's men.
Herold Goulon was sent off for two bookings. Defeat for Rovers means they have not won away in five matches.