Watford booked their place in the last eight of the FA Cup after Scott Wootton's own goal handed them a 1-0 victory over Leeds at Vicarage Road.
It took Quique Sanchez Flores' side until the 54th minute to break down their Championship opponents on Saturday, when Wootton turned Ben Watson's cross into his own net.
The hosts thought they had wrapped up the win when Etienne Capoue bundled the ball home at the far post, only to see referee Michael Oliver rule out the goal for a push from Troy Deeney.
Watford, who brought on Odion Ighalo with just under 25 minutes remaining, pushed for a second throughout the second half as they looked to make the game safe, but in the end it was not needed as the Premier League side reached the quarter-finals for the first time since 2007.
Flores' side, who made six changes from the side that beat Crystal Palace in the Premier League, looked to assert their dominance over Leeds early and they nearly took the lead in the first minute, but Deeney's header was deflected wide.
Leeds were slow out of the blocks but the hosts could not take advantage as Miguel Britos headed over not once but twice, as Watson's corners continued to cause problems for Steve Evans' side.
The hosts pushed forward in search of an opener as Jose Holebas's drilled effort was deflected wide, before Capoue, Mario Suarez and Almen Abdi all missed half chances.
In the 26th minute, Leeds finally made an attack of note as Mirco Antenucci turned into space on the halfway line before driving to the edge of the Watford area and picking out Stuart Dallas, whose shot lacked the power necessary to trouble Costel Pantilimon.
However, the move seemed to rouse Leeds and their excellent travelling support as Dallas dragged wide from the edge of the box on two occasions, either side of Marco Silvestri keeping out Juan Carlos Paredes' low cross for the hosts.
After the break, Watford came flying out the traps as Deeney saw two shots blocked in quick succession, before Holebas' shot was somehow kept out at the far post by more excellent defending.
The home side finally made the breakthrough 10 minutes after the restart when Wootton could not get out of the way of Watson's cross at the far post and the ball rebounded off the defender and into the back of the net.
Minutes later, Abdi fired over the bar before Capoue's goal was ruled out for Deeney's push on Charlie Taylor in the six-yard box, as the hosts looked to give themselves breathing space.
Nothing much was coming back from Leeds as Evans drew a frustrated figure on the touchline and it was Watford who continued to push for a second, but Capoue could only fire over the bar in the final few minutes after excellent link-up play with Deeney.
Leeds, with their only real attack of the second half, had a final chance of an equaliser in the 89th minute, but Souleymane Doukara saw his shot sail over the crossbar as Watford reached the last eight.