Huddersfield finally wrapped up the win in the closing minutes, though, when Mooy doubled his tally from the penalty spot following Doucoure's foul on Depoitre.
Wagner heaped praise on Watford, ranking them alongside Leicester as the next best teams outside the traditional top six and insists his players are not thinking about Saturday's opponents recent poor form.
Huddersfield have failed to win any away games since the opening day of the season, and they are now experiencing a goalscoring drought of ten hours while on the road from the John Smith's stadium.
Huddersfield's second goal came after Watford's defence switched off.
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Watford forward Troy Deeney was then sent off before the break for a rash challenge on Collin Quaner.
The only blemishes for Huddersfield were injuries to Kachunga and defender Chris Loewe, who limped off before halftime. Chris Loewe got a knock on his foot.
"I would say if Watford didn't get the red card I am unsure if we would get a second yellow for Hogg", Wagner added.
Depoitre's goal five minutes after the restart appeared to have taken the game away from Watford, though Hogg's red card - and a stunning strike from Abdoulaye Doucoure - seemed to give the Hornets a chance.
With this victory, the Terriers climb to 11th on the log with 21 points from 18 games.