Troy Deeney's brace in his 100th game for Watford helped the Hornets win their fifth Championship game in seven, and leave Barnsley winless in nine.
The striker's first, a 10th minute header, was added to by a clinical Mark Yeates finish after half-time.
Deeney's second from 16 yards and a Matej Vydra penalty sealed the win.
Marcus Tudgay struck late on but it proved little consolation for the visitors, who are now only two points clear of the bottom three.
Deeney's seventh and eighth goals of the campaign demonstrated the good form the forward is in, and why Watford boss Gianfranco Zola opted to promote him from the substitutes' bench.
The Italian manager's selection paid early dividends, with the 24-year-old able to create time and space for himself inside the Barnsley box on 10 minutes.
The striker then rose largely unopposed to convert Marco Cassetti's corner, the fourth time in three matches that the visitors had conceded from a set-piece.
Watford's recent good form
- Sat 1 Dec: Watford 4-1 Barnsley
- Tue 27 Nov: Sheff Wed 1-4 Watford
- Sat 24 Nov: Blackpool 2-2 Watford
- Sat 17 Nov: Watford 2-1 Wolves
- Sat 10 Nov: Leeds United 1-6 Watford
- Tue 6 Nov: Watford 0-0 Millwall
- Sat 3 Nov: Watford 2-1 Leicester
Barnsley rallied, though, and went close with chances following a pair of Akos Buzsaky corners, but neither Craig Davies nor Tudgay were able to capitalise.
And the Tykes were punished after the interval when midfielder Yeates received the ball at a very tight angle before brilliantly finding the bottom corner of Luke Steele's net.
That strike spurred on the hosts, on-loan Udinese forward Fernando Forestieri teeing up Deeney for his well-taken second.
Hornets substitute Vydra rounded off a one-sided second half by converting an 83rd minute penalty after he had been hacked down from behind by Jimmy McNulty.
Barnsley's Tudgay scored his second goal in as many matches with a smart finish in stoppage-time, but it counted for little as Watford climbed to sixth in the table.
Watford manager Gianfranco Zola:
"Obviously we are delighted.
"There's a good atmosphere at the ground with the players and with the supporters.
"But we need to make sure we keep the balance because there's a long, long way to go and this Championship you cannot afford to lose concentration."
Barnsley manager Keith Hill:
"We made some horrendous decisions in and out of possession. The best team won and I've got to congratulate Gianfranco because I think he's got an excellent side.
"We looked weak against the opposition so I don't think we were ever in the game. Individually and collectively, we weren't cohesive today, with and without the ball."
Live Text Commentary
Full Time The game is over, as the referee blows his whistle.90:00 +3:34 Goal scored
Goal! - Marcus Tudgay - Watford 4 - 1 Barnsley Marcus Tudgay finds the net with a goal from deep inside the penalty box to the bottom right corner of the goal. Watford 4-1 Barnsley.90:00 +2:04
Free kick awarded for a foul by Stephen Foster on Matej Vydra. Shot comes in from Mark Yeates from the free kick.90:00 +1:40
Matej Vydra takes a shot. Blocked by Stephen Foster.90:00 +1:20
The ball is swung over by Scott Golbourne, Joel Ekstrand manages to make a clearance.90:00 +1:01
The ball is swung over by Jim O'Brien, Joel Ekstrand manages to make a clearance.85:42
Alexandre Geijo concedes a free kick for a foul on Scott Golbourne. Jimmy McNulty restarts play with the free kick.84:48
Mark Yeates takes the outswinging corner, Joel Ekstrand produces a header from inside the area that goes over the crossbar.84:26
Joel Ekstrand takes a shot. Save by Luke Steele.82:34 Goal scored
Goal! - Matej Vydra - Watford 4 - 0 Barnsley Penalty taken right-footed by Matej Vydra and scored. Watford 4-0 Barnsley.81:56
Foul by Jimmy McNulty on Matej Vydra, Penalty awarded.80:23 Substitution
Substitution Troy Deeney goes off and Alexandre Geijo comes on.80:23 Substitution
Substitution Jim O'Brien joins the action as a substitute, replacing Jonathan Greening.80:03
Marco Cassetti takes a shot from a long way out which goes wide of the right-hand post.78:47
Jonathan Hogg gives away a free kick for an unfair challenge on Stephen Foster. Jimmy McNulty takes the direct free kick.77:10
The ball is crossed by Stephen Dawson, Manuel Almunia makes a clearance.76:06
Stephen Dawson takes a shot. Comfortable save by Manuel Almunia.75:26
Troy Deeney takes a shot. Save by Luke Steele.73:09
The ball is swung over by Daniel Pudil, Header by Tommie Hoban from deep inside the penalty area misses to the left of the target.72:20
Akos Buzsaky takes a shot. Save by Manuel Almunia.
Scott Golbourne delivers the ball, Tommie Hoban manages to make a clearance.70:31 Substitution
Substitution Cristian Battocchio on for Nathaniel Chalobah.69:03 Substitution
Substitution Reuben Noble-Lazarus on for Emile Sinclair.69:03
Shot from just outside the area by Troy Deeney goes over the bar.66:53
Free kick awarded for a foul by Craig Davies on Daniel Pudil. Manuel Almunia takes the free kick.65:08 Substitution
Substitution Fernando Forestieri leaves the field to be replaced by Matej Vydra.65:08
Fernando Forestieri provided the assist for the goal.65:08 Goal scored
Goal! - Troy Deeney - Watford 3 - 0 Barnsley Troy Deeney gets on the score sheet with a goal from just outside the penalty box to the bottom left corner of the goal. Watford 3-0 Barnsley.64:49
Fernando Forestieri fouled by Martin Cranie, the ref awards a free kick. Fernando Forestieri takes the direct free kick.63:12
Inswinging corner taken right-footed by Akos Buzsaky from the left by-line to the near post, clearance made by Manuel Almunia.62:32
Martin Cranie sends in a cross, Marco Cassetti manages to make a clearance.62:10
Marcus Tudgay delivers the ball, clearance by Fitz Hall.58:55 Goal scored
Goal! - Mark Yeates - Watford 2 - 0 Barnsley Mark Yeates gets on the score sheet with a goal from close in to the bottom right corner of the goal. Watford 2-0 Barnsley.58:01
Free kick awarded for an unfair challenge on Daniel Pudil by Craig Davies. Free kick taken by Manuel Almunia.56:59
The ball is swung over by Scott Golbourne, Shot by Emile Sinclair from deep inside the penalty area misses to the right of the target.56:33
Centre by Jonathan Greening, clearance by Daniel Pudil.56:10
Corner taken short by Akos Buzsaky.55:20
The official flags Fernando Forestieri offside. Stephen Foster takes the indirect free kick.54:07
The ball is sent over by Akos Buzsaky, free kick awarded for a foul by Craig Davies on Daniel Pudil. Manuel Almunia takes the direct free kick.52:58
The ball is sent over by Martin Cranie, clearance made by Fitz Hall.52:12
Fernando Forestieri handles the ball and concedes a free kick. Stephen Foster restarts play with the free kick.51:14
Mark Yeates takes the outswinging corner, Headed effort from inside the area by Tommie Hoban misses to the left of the target.49:46
Outswinging corner taken by Akos Buzsaky from the right by-line played to the near post, Effort on goal by Marcus Tudgay from inside the penalty area goes harmlessly over the bar.49:21
Outswinging corner taken by Akos Buzsaky from the right by-line played to the near post, Joel Ekstrand manages to make a clearance.48:22
Scott Golbourne sends in a cross, clearance made by Fitz Hall.48:02
Stephen Dawson crosses the ball, Joel Ekstrand manages to make a clearance.46:02
Free kick awarded for a foul by Mark Yeates on Marcus Tudgay. Akos Buzsaky has a direct shot on goal from the free kick.45:37
The ball is swung over by Martin Cranie, Fitz Hall makes a clearance.45:01
The match restarts for the second half.45:00 +2:07 Half time
Half Time The whistle is blown to end the first half.45:00 +1:35
The ball is crossed by Marco Cassetti, Jonathan Greening manages to make a clearance.45:00 +0:27
Joel Ekstrand fouled by Craig Davies, the ref awards a free kick. Manuel Almunia takes the free kick.45:00 +0:10
Joel Ekstrand challenges Scott Golbourne unfairly and gives away a free kick. Scott Golbourne restarts play with the free kick.44:34
Centre by Daniel Pudil, Fernando Forestieri takes a shot.43:09
Unfair challenge on Daniel Pudil by Stephen Dawson results in a free kick. Manuel Almunia restarts play with the free kick.39:39
Foul by Craig Davies on Nathaniel Chalobah, free kick awarded. Fitz Hall takes the free kick.38:29
Emile Sinclair takes a shot. Tommie Hoban makes a clearance.36:24
Inswinging corner taken by Akos Buzsaky from the left by-line, Manuel Almunia makes a clearance.36:04
Stephen Dawson takes a shot. Blocked by Jonathan Hogg.35:21
Corner taken by Akos Buzsaky from the right by-line to the near post.33:29
Akos Buzsaky takes a outswinging corner from the right by-line to the near post, clearance by Troy Deeney.32:29
The assistant referee signals for offside against Fernando Forestieri. Stephen Foster restarts play with the free kick.31:13 Substitution
Substitution Stephen Dawson comes on in place of Jacob Mellis.31:13
Troy Deeney gives away a free kick for an unfair challenge on Stephen Foster. Jimmy McNulty takes the direct free kick.30:55
Troy Deeney takes a shot. Stephen Foster gets a block in.29:25
Daniel Pudil has an effort at goal from just inside the box that misses to the right of the goal.29:03
Marco Cassetti sends in a cross, Martin Cranie manages to make a clearance.27:43
Inswinging corner taken right-footed by Mark Yeates played to the near post, Marco Cassetti takes a shot.27:17
Troy Deeney takes a shot. Martin Cranie gets a block in.26:23
The ball is swung over by Nathaniel Chalobah, save made by Luke Steele.24:16
Mark Yeates takes the inswinging corner, Effort on goal by Joel Ekstrand from deep inside the penalty area misses to the right of the target.23:59
Fernando Forestieri takes a shot. Save by Luke Steele.22:38
Troy Deeney takes a shot. Blocked by Jimmy McNulty.18:25
Corner taken by Akos Buzsaky, Craig Davies takes a shot. Inswinging corner taken right-footed by Akos Buzsaky from the right by-line, Emile Sinclair takes a shot. Save made by Manuel Almunia. Outswinging corner taken from the right by-line by Akos Buzsaky, Troy Deeney manages to make a clearance. Save by Manuel Almunia.17:46
Akos Buzsaky has an effort at goal from just outside the box which goes wide of the right-hand upright.16:21
Mark Yeates takes a inswinging corner from the left by-line played to the near post, clearance by Luke Steele.15:37
Troy Deeney fouled by Stephen Foster, the ref awards a free kick. Free kick crossed right-footed by Mark Yeates from right channel, clearance by Jonathan Greening.14:26
The ball is crossed by Martin Cranie, Tommie Hoban manages to make a clearance.14:04
Martin Cranie crosses the ball, clearance by Tommie Hoban.13:16
Marco Cassetti sends in a cross, Martin Cranie makes a clearance.13:04
The ball is delivered by Fernando Forestieri.12:18
Stephen Foster fouled by Troy Deeney, the ref awards a free kick. Free kick taken by Stephen Foster.11:33
Effort from outside the penalty box by Akos Buzsaky goes wide left of the target.9:24
Assist by Marco Cassetti.9:24 Goal scored
Goal! - Troy Deeney - Watford 1 - 0 Barnsley Troy Deeney scores a headed goal from close range. Watford 1-0 Barnsley.9:12
Inswinging corner taken by Marco Cassetti from the left by-line,8:57
Nathaniel Chalobah crosses the ball, Craig Davies makes a clearance.8:24
Fernando Forestieri takes a shot. Blocked by Stephen Foster.6:08
The ball is crossed by Craig Davies, save by Manuel Almunia.5:04
Outswinging corner taken by Mark Yeates, Tommie Hoban takes a shot. Save made by Luke Steele.3:50
Marco Cassetti takes a shot. Save by Luke Steele. Emile Sinclair takes a shot. Save made by Manuel Almunia.2:58
Free kick awarded for an unfair challenge on Joel Ekstrand by Marcus Tudgay. Direct free kick taken by Manuel Almunia.0:00
The game kicks-off.
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