Match ends, Watford 1, Leeds United 0.
Watford reached the FA Cup quarter-finals for the first time since 2007 after Scott Wootton's own goal gifted them victory against Leeds.
The visiting defender miscued an attempted clearance into his own net shortly after the interval.
Watford, who made six changes, just about deserved victory, with Miguel Britos and Almen Abdi going close and Etienne Capoue having a goal ruled out.
Leeds' best moment came when Stuart Dallas curled a low effort wide.
But it was a largely disappointing display from the Yorkshire side, who have not made the last eight of the FA Cup since 2003.
Wootton's moment of madness
Although they were limited in attack, Leeds had defended stoutly for 53 minutes - restricting Watford to just one shot on target - and the match looked to be petering out to an inevitable replay.
But that was before Wootton's inexplicable intervention.
Ben Watson's cross had eluded everyone and was curling harmlessly out of danger when Wootton - playing out of position at right-back - attempted to touch it behind and instead succeeded only in slicing it comically into his own net.
The 24-year-old was visibly distraught, burying his head in his hands and having to be consoled by team-mate Giuseppe Bellusci, and manager Steve Evans said after the match it was "probably the lowest point of Wootton's life".
With Leeds toothless going forward, the former Manchester United youngster's error was always likely to prove decisive.
Watford fringe players fail to shine
Hornets boss Quique Sanchez Flores handed an opportunity to several of his reserve players, with striker Nordin Amrabat and midfielder Mario Suarez - signed in January for £6m and £4m respectively - among those brought in.
But the new players failed to catch the eye, with Moroccan international Amrabat having just one shot and 28 touches - 26 fewer than any other Watford outfield starter.
Suarez was scarcely more impressive in the centre of the park - winning only 40% of his duels - while goalkeeper Costel Pantilimon, replacing Heurelho Gomes, barely had a save to make.
Instead, it was regular midfielders Ben Watson and Capoue - who saw a goal chalked off for an off-the-ball push by Troy Deeney - who were by far Watford's most impressive performers.
Man of the match - Ben Watson
What they said
Watford manager Quique Sanchez Flores: "To win the match is the most important thing for us, and to avoid a replay for us. We were better in the second half than the first half. We took control with the ball and we had more attempts."
Flores on midfielder Suarez and striker Amrabat, handed rare starts: "They are completely ready to be protagonists in the team, they are very important players."
Leeds manager Steve Evans: "I think the performance was good. It was the cruellest way ever to go out of the FA Cup - it was a terrible goal to concede. We dominated the quality of the play until half-time. If you came here in the first half, you'd have thought Leeds United were the Premier League team.
"Scott Wootton's in tears, he's apologised to every member of staff and he'll not sleep for days.
"The time wasting [by Watford] was like something you'd see abroad, you don't want to see that in English football."
The stats you need to know
- Troy Deeney failed to score against Leeds for the first time in his last five meetings against them.
- Leeds failed to score in the FA Cup for the fourth time in their last six games
- Quique Sanchez Flores has now overseen 1-0 wins in all three of his FA Cup matches in charge
- Leeds have only kept one clean sheet in their last 14 FA Cup games.
Both sides return to league action: Watford take on Bournemouth on Saturday, while Leeds host Fulham on Tuesday.
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- 14ParedesBooked at 32mins
- 15CathcartBooked at 67mins
- 29CapoueSubstituted forAnyaat 90+1'minutes
- 22AbdiSubstituted forGuédiouraat 77'minutes
- 11N AmrabatSubstituted forIghaloat 67'minutes
- 5BellusciBooked at 24mins
- 15DallasSubstituted forMowattat 61'minutes
- 16DiagouragaSubstituted forBotakaat 86'minutes
- 26BridcuttBooked at 52mins
- 23L Cook
- 7AntenucciSubstituted forErwinat 83'minutes
- Michael Oliver
- Shots on Target
Second Half ends, Watford 1, Leeds United 0.
Offside, Leeds United. Souleymane Doukara tries a through ball, but Lee Erwin is caught offside.
Attempt blocked. Souleymane Doukara (Leeds United) right footed shot from the left side of the box is blocked.
Attempt blocked. Ben Watson (Watford) right footed shot from outside the box is blocked. Assisted by Troy Deeney.
Odion Ighalo (Watford) wins a free kick in the attacking half.
Foul by Scott Wootton (Leeds United).
Attempt missed. Giuseppe Bellusci (Leeds United) right footed shot from more than 35 yards misses to the right. Assisted by Liam Bridcutt.
Offside, Leeds United. Giuseppe Bellusci tries a through ball, but Souleymane Doukara is caught offside.
Substitution, Watford. Ikechi Anya replaces Etienne Capoue.
Offside, Watford. Craig Cathcart tries a through ball, but Odion Ighalo is caught offside.
Attempt missed. Souleymane Doukara (Leeds United) left footed shot from the left side of the box is too high. Assisted by Scott Wootton.
Etienne Capoue (Watford) wins a free kick on the left wing.
Foul by Sol Bamba (Leeds United).
Substitution, Leeds United. Jordan Botaka replaces Toumani Diagouraga.
Attempt missed. Etienne Capoue (Watford) right footed shot from the centre of the box is too high. Assisted by Troy Deeney following a fast break.
Substitution, Leeds United. Lee Erwin replaces Mirco Antenucci.
Offside, Leeds United. Scott Wootton tries a through ball, but Alex Mowatt is caught offside.
Foul by Troy Deeney (Watford).
Toumani Diagouraga (Leeds United) wins a free kick on the right wing.