A Scott Wootton own goal was enough to steer Watford into the FA Cup quarter-finals for the first time since 2007 as Leeds United were beaten 1-0 at Vicarage Road.
Wootton was under little pressure at the back post when he diverted Ben Watson's whipped centre past his own goalkeeper eight minutes into the second half.
Watford had the ball in the net again shortly after, but Etienne Capoue's neat finish was chalked off for a Troy Deeney foul.
A third clean sheet in their last four home outings in all competitions helped Watford progress in the first FA Cup meeting between these teams and the Premier League side will have one eye on a trip to Wembley as well as securing their top-flight status.
Quique Sanchez Flores made six changes from Watford's 2-1 win at Crystal Palace last weekend, with top scorer Odion Ighalo among those rested. A dead leg ruled out Liam Cooper and Leeds manager Steve Evans replaced the defender with Sol Bamba.
The hosts, yet to win the FA Cup, had two early sights of goal, captain Deeney having a header deflected wide in the first minute before Miguel Britos saw his own header fly well over.
Nordin Amrabat looped a header into Marco Silvestri's arms before Britos had a big chance at the back post, but the defender put another header wide as Watford dominated aerially.
Jose Holebas saw his strike deflect just wide as the Premier League side cranked up the pressure, with the visitors' first chance arriving against the run of play after 25 minutes.
A terrific counter-attack led by Mirco Antenucci worked an opening for Stuart Dallas, but his tame shot was saved easily by Costel Pantilimon. Dallas then dragged wide after brilliant build-up play by Souleymane Doukara.
Dallas saw another effort deflect wide shortly before half-time as the Championship side, who have now won just three of their last 12 matches in all competitions, continued to grow into the contest.
But any momentum that Leeds were gaining came to a halt as Watford broke the deadlock shortly after the interval, Wootton inadvertently turning Watson's excellent cross into his own net.
Capoue thought he had doubled Watford's lead after 57 minutes when he beat Silvestri from close range, but referee Michael Oliver disallowed it for a push by Deeney.
Liam Bridcutt tested Pantilimon when he let fly with a long-range drive after 64 minutes and, with two minutes to go, Doukara lashed a shot over after being played in by Wootton, but Leeds were unable to find an equaliser.