The margin of victory should have been more convincing but Watford will travel to the winners of tomorrow night’s replay between Manchester City and Blackburn Rovers in the FA Cup fourth round after beating Bristol City 2-0 in their own replay at Vicarage Road tonight.
The Robins had the better of what few good chances there were in the first half but it was the Hornets who led at the break when Davide Faraoni was credited with the goal following a corner, even though the last touch came off defender Karleigh Osborne.
Lewis McGugan added the crucial second goal after the break and then a combination of good goalkeeping and poor finishing prevented the Hornets from providing further gloss on the scoreline. But there was to be another bonus for the home side - aside from recording only their second win in 15 league and cup outings - in that they were able to welcome back second-half substitute Almen Abdi, who had been sidelined since the end of August.
Beppe Sannino shuffled his pack, making seven changes to the team which lost at home to Reading opn Saturday but arguably the most heartening news was on the bench with the inclusion of Abdi in a match-day 18 for the first time in more than four months.
The changes to the team saw Jonathan Bond, Fitz Hall, Cristian Battocchio and Iriney all come in, Faraoni and Fernando Forestieri make their first starts following their respective injury problems and Ikechi Anya was also back after his lay-off and went straight into the starting XI.
Hector Bellerin and Alexander Merkel were ineligible, with the latter also suspended, while Manuel Almunia, Lloyd Doyley, Sean Murray, Daniel Pudil and Diego Fabbrini dropped to the bench.
Steve Cotterill made three changes to the side which drew 1-1 at Bradford City last time out with Liam Fontaine, Brendan Moloney and Joe Bryan replacing Derrick Williams, Greg Cunningham and Scott Wagstaff, all of whom were among the substitutes.
The Hornets, who were attacking the Rookery in the first half, lined up slightly unexpectedly at the back with Gabriele Angella on the right of the defensive trio and Hall in the middle.
But the hosts looked far from convincing at the back in the second minute when they were fortunate not to go behind as Jay Emmanuel-Thomas slid a pass through to Sean Baldock to put him one-on-one with Bond but the Hornets keeper stood up well, forcing the Robins skipper to make a decision and in the end he fired straight at the England Under-21 international.
The home side gradually began to settle though, and had their first effort in the seventh minute when Lewis McGugan fired straight at Elliot Parish from around 20 yards out.
The Hornets threatened again when McGugan advanced before slipping in Forestieri, who was preparing to pull the trigger when Aiden Flint superbly nicked the ball away from him and the Hornets forward went to ground very optimistically seeking a penalty.
City were the more composed side in the opening 15 minutes though, and their next opening came when Baldock flicked a header over the top from around eight yards out after Flint, who had stayed upfield following a free-kick, headed a Bryan delivery from the left back into the heart of the area.
Watford had a promising situation when Battocchio lifted the ball out to Forestieri on the right side of the penalty area and his great touch took him away from a defender before laying it inside. McGugan then dummied for Deeney, which put him off slightly, but he still managed to trap the ball and tried to play in Anya to his left but he was unable to control.
Anya then had a shot blocked but this was part of a reasonable spell for the home side which continued with two corners being won.
The first saw Deeney get a near-post flick on a delivery from the right which went all the way across the face of goal but the second saw the Hornets take the lead, albeit in rather confusing circumstances.
The ball was touched on when it was played in from the right and it travelled to beyond the far post where Faraoni scuffed it back goalwards and, after some deliberation, it was deemed that Osborne had only succeeded in hitting the ball into his own as he tried to clear. However, the Italian was still credited with the goal.
Little of attacking note then happened until shortly before the interval when there was a flurry of action in the final two minutes of the half.
First Bond had to drop sharply to his right to hold onto a well-struck Emmanuel-Thomas effort before the play switched to the other end where Forestieri saw a shot from the left side of the area deflected across the face of goal and behind.
But the best chance was to fall to City in stoppage time when they broke and the galloping Osborne managed to squeeze in a low centre from the right but Ekstrand did superbly to get across Bobby Reid and force him to lift the ball over the top from close range.
The visitors were quickly out of the traps at the start of the second half and within the first 30 seconds, a Marlon Pack drive from 25 yards was destined for the bottom corner until Bond got down well to push it behind.
In the 49th minute, Angella showed what an accomplished footballer he is when, after the ball had been worked from left to right across halfway, the defender played a nice give-and-go with Faraoni off the right flank and, as the pitched opened up in front of him, he advanced before curling a left-footed shot narrowly wide from 20 yards.
Watford were in again moments later when Anya got round the back of the defence and laid the ball across and it broke for Faraoni who, under pressure, lifted his shot over the target.
The Hornets needed the comfort of a second goal and they had a set-piece opportunity to get one in the 63rd minute when they were awarded a free-kick 25 yards out. McGugan got his strike around the wall and on target but Elliot Parish was always behind it.
With his next opportunity barely a minute later though, the Hornets midfielder made no mistake.
After Deeney had been outnumbered on the left side of the area, the ball broke for McGugan who drove purposefully forward before drilling a left-footed shot past Parish to make it 2-0.
The visitors might have caused the visitors some discomfort when they awarded a free-kick 20 yards out after Emmanuel-Thomas was tripped by Battocchio 20 yards out, but the striker could only hit the top of the wall with his set piece.
Watford immediately broke with McGugan leading the charge downfield, he slipped in Anya to his left but he chose to go it alone with Forestieri screaming for the ball inside him and the Scottish international’s left-foot shot was pushed into the side netting by Parish.
That was a good save but even better was to follow moments later when he somehow foiled Deeney from close range when the striker looked odds-on to score after being picked out by Forestieri.
McGugan also dragged a reasonable opening wide but that was his last meaningful involvement before he was replaced in the 75th minute and those of a yellow affiliation inside Vicarage Road stood as one to applaud the return of Abdi.
Deeney was denied by Parish in more routine fashion before Angella was booked for a foul and then Cotterill made a triple change, bringing on Wagstaff, Cunningham and Wes Burns for Bryan, Baldock and Moloney.
But Watford really should have made the tie absolutely safe when Abdi released Battocchio ahead of him and he slid in Forestieri, who contrived to drag his finish wide of the near post from ten yards with only the keeper to beat.
After Wagstaff had been booked for throwing the ball away, Anya was replaced by Pudil but the Hornets saw out the closing stages to secure their fourth round place.
Watford: Bond; Angella, Hall, Ekstrand; Faraoni, Battocchio, Iriney, McGugan (Abdi 75), Anya (Pudil 86); Forestieri, Deeney. Not used: Almunia, Doyley, Murray, Fabbrini, Nosworthy.
Bristol City: Parish; Osborne, Flint, Fontaine; Moloneym (Wagstaff 78), Elliott, Reid, Pack, Bryan (Cunningham 78); Emmanuel-Thomas, Baldock (Burns 78). Not used: Fielding, Williams, Carey, Wynter.
Bookings: Angella for a foul (78); Wagstaff for dissent (84).
Attendance: 7,302 (1,129 away).
Referee: Darren Drysdale.