Deeney, who was making 100th appearance for Watford, hit the bar for the home side before he had another effort cleared off the line.
Simon Grayson's team failed to heed the warning and handed the home side the perfect opportunity to open the scoring from the penalty spot and Deeney made no mistake.
Gianfranco Zola's men, who are the division's leading scorers, quickly added to their tally when Vydra stretched to meet an inviting cross from Cassetti.
He then made sure of the points when he scored his 16th goal of the season after Deeney this time turned provider and sent him clear.
Huddersfield, who now sit 18th in the Championship table, offered little in attack and Battocchio completed the scoring with a lovely flick into the back of the net with the outside of his boot.
Watford manager Gianfranco Zola:
"I just found out that this morning more than 100 supporters turned up here to help clear the pitch of the snow, so I think they've been rewarded with this performance and they deserved it.
"I think we've played some better games than this but it was a mature game. The result is a little bit too hard towards Huddersfield because in the first half they made it very, very difficult for us, so we had to work hard.
"I think the goal towards the end of the first half helped the team a lot because we then, in the second half, managed to play the football that we want to play. They had to open up a little bit more."
Huddersfield boss Simon Grayson:
"I thought, first half, we were well and truly in the game. We kept them quiet, you could sense the atmosphere had gone quiet as well and the decision just before half time changed the game.
"We let it affect us and it obviously gave them a big confidence boost. The decision was wrong, it's great tackle by our right back and it's outside the box, so it's a poor decision.
"But in the second half we felt sorry for ourselves and allowed Watford to dictate the game and when you do that against a team like Watford then you're under pressure because they're a good side."
Live text and stats
Saturday, 19 January 2013
Deeney (pen) 45+8
27 Cassetti yellow card
39 Chalobah (Eustace 61)
09 Deeney (Geijo 84)
20 Vydra (Forestieri 76)
37 Mujangi Bia,
02 Woods yellow card
05 P Clarke
08 Clayton (Southern 46)
07 Scannell (Arfield 79)
18 Vaughan yellow card (Novak 57)
Ref: DuncanAtt: 12,522
Attempts on target
Attempts off target
90:00+4:09 The referee ends the match.
90:00+3:54 Almen Abdi produces a cross, Keith Southern makes a clearance.
90:00+2:01 Close range shot by Fernando Forestieri goes wide of the left-hand post.
90:00+1:09 The assistant referee flags for offside against Fernando Forestieri. Anthony Gerrard takes the direct free kick.
89:32 Fernando Forestieri fouled by Calum Woods, the ref awards a free kick. Direct free kick taken by Craig Forsyth.
88:28 Corner taken by Jack Hunt.
88:18 The ball is delivered by Paul Dixon, Joel Ekstrand manages to make a clearance.
85:38 Assist on the goal came from Marco Cassetti.
85:38 GOAL - Cristian Battocchio:Watford 4 - 0 Huddersfield A goal is scored by Cristian Battocchio from deep inside the penalty area to the bottom left corner of the goal. Watford 4-0
85:27 Centre by Marco Cassetti,
84:14 A cross is delivered by Almen Abdi, Close range headed effort by Alexandre Geijo misses to the right of the target.
83:36 Short corner worked by Fernando Forestieri.
83:36 Substitution Alexandre Geijo joins the action as a substitute, replacing Troy Deeney.
83:23 Craig Forsyth crosses the ball, blocked by Calum Woods.
82:46 The ball is sent over by Lee Novak, blocked by Nyron Nosworthy.
82:28 The assistant referee signals for offside against Fernando Forestieri. Direct free kick taken by Peter Clarke.
79:22 Jack Hunt delivers the ball.
78:13 Substitution Sean Scannell goes off and Scott Arfield comes on.
75:00 Substitution Matej Vydra leaves the field to be replaced by Fernando Forestieri.
73:47 The assist for the goal came from Troy Deeney.
73:47 GOAL - Matej Vydra:Watford 3 - 0 Huddersfield Matej Vydra scores a goal from inside the penalty area low into the middle of the goal. Watford 3-0 Huddersfield.
69:28 A cross is delivered by Paul Dixon, save made by Manuel Almunia.
68:37 Free kick awarded for an unfair challenge on Jack Hunt by Craig Forsyth. Calum Woods restarts play with the free kick.
66:52 Lee Novak is ruled offside. Manuel Almunia takes the free kick.
66:04 Inswinging corner taken right-footed by Neil Danns from the left by-line to the near post, save by Manuel Almunia.
65:56 The ball is swung over by Jack Hunt, Marco Cassetti makes a clearance.
65:28 Corner taken by Neil Danns from the left by-line to the near post, Matej Vydra makes a clearance.
64:22 Cristian Battocchio has shot on goal from just outside the penalty box which goes wide of the right-hand upright.
63:01 Almen Abdi takes a outswinging corner to the near post, Keith Southern manages to make a clearance.
61:19 The ball is sent over by Calum Woods, Jermaine Beckford takes a shot. Save by Manuel Almunia.
60:21 Substitution Nathaniel Chalobah leaves the field to be replaced by John Eustace.
60:08 Centre by Cristian Battocchio, Paul Dixon manages to make a clearance.
59:17 Neil Danns takes a shot. Save by Manuel Almunia.
58:57 The ball is swung over by Sean Scannell, clearance by Craig Forsyth.
58:49 Calum Woods produces a cross.
57:33 Matej Vydra has an effort at goal from deep inside the area missing to the right of the target.
56:50 Substitution Lee Novak comes on in place of James Vaughan.
56:05 The assist for the goal came from Marco Cassetti.
56:05 GOAL - Matej Vydra:Watford 2 - 0 Huddersfield Matej Vydra scores a goal from inside the six-yard box to the top left corner of the goal. Watford 2-0 Huddersfield.
55:47 A cross is delivered by Marco Cassetti,
53:57 Nathaniel Chalobah fouled by Jermaine Beckford, the ref awards a free kick. Joel Ekstrand restarts play with the free kick.
53:33 Neil Danns concedes a free kick for a foul on Nathaniel Chalobah. Free kick taken by Nathaniel Chalobah.
49:11 Foul by Craig Forsyth on Jack Hunt, free kick awarded. Free kick taken by Alex Smithies.
45:01 The match restarts for the second half.
45:01 Substitution Keith Southern comes on in place of Adam Clayton.
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