The visitors had started brightly at Vicarage Road as Aaron Mooy tested Ben Foster from distance and Alex Pritchard sent a curling effort narrowly over the crossbar inside the opening minutes.
Foster was forced to tip Chris Lowe’s long-range drive on to the bar midway through the first half, but Isaac Success added a third for Watford late on to secure a comfortable victory for Javi Gracia’s men.
The defeat means Huddersfield slip to the foot of the Premier League table, with Newcastle climbing to 19th following their goalless draw at Southampton.
Watford move on to 19 points, surpassing their 17-point haul after 10 games of the 1982-83 season, when they finished runners-up to Liverpool.
Watford were one of only two teams to lose twice to Huddersfield last season – including a 4-1 defeat at home – but two magnificent goals inside the opening 20 minutes put the Hornets firmly in command on Saturday.
Pereyra’s opener was a sensational effort, the Argentine collecting the ball on the left flank then waltzing through five Huddersfield challenges before sending a composed finish past goalkeeper Lossl.
The hosts’ second was no less spectacular as Deulofeu found the far corner from a tight angle following another weaving run through a static Terriers defence.
The former Barcelona and Everton forward could have doubled his personal tally in the second half, but he scuffed his shot wide after rounding the onrushing Lossl.
It did not matter, however, as Success tapped home his first Premier League goal of the season to put the seal on a convincing victory.
The defeat extends Huddersfield’s winless run in the league to 14 matches, with their last victory coming at home to Watford on 14 April.
Wagner’s side created the better opportunities in the first half, with Mooy twice forcing Foster into action and Pritchard narrowly missing the target from a tight angle.
Lowe went closest for the visitors with a stinging effort from distance, which Foster did well to tip on to the crossbar.
Huddersfield registered more attempts on target than their hosts in the match – seven compared to Watford’s six – but their lack of goals is fast becoming a major cause for concern.
The Terriers have scored just four in their 10 league matches so far – fewer than any other club in the division.
Taking three points at home to fellow strugglers Fulham in their next encounter on 5 November would go a long way towards lifting the gloom at the John Smith’s Stadium.
