Spanish forward Gerard Deulofeu, who replaced Isaac Success in the Watford starting lineup, slipped past two Cardiff defenders in the box before drilling a finish past goalkeeper Neil Etheridge to give the hosts an early lead.
With momentum firmly on their side, Watford created further chances through Roberto Pereyra but Etheridge kept the away side in the contest with two spectacular saves just before halftime.
Watford returned from the break with no signs of complacency as Deulofeu's perfectly weighted pass found full back Jose Holebas, who curled a superb effort into the top corner to make it 2-0.
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Portuguese midfielder Domingos Quina then netted his first Premier League goal from the edge of the box as Watford edged closer to a convincing victory at Vicarage Road.
But Cardiff roared back into the match when forward Junior Hoilett fired a curling effort past goalkeeper Ben Foster.
The Welsh side could sniff an unlikely draw when Bobby Reid scored to make it 3-2 in the 82nd minute but Watford held their nerve to record a first league success in seven matches.
DESEERVED WIN
"The last games we have played well, but today we deserved the win, it is important for the players and supporters," said Watford boss Javi Gracia. "All of them deserve the victory."
The Hornets had more than 70 percent possession and took 17 shots, showing glimpses of the attacking fluidity which earned them four straight league wins at the start of the campaign.
But Gracia expects his mid-table team, who now have 24 points, to shut the door on their opponents, having controlled the majority of the game.
"We dominated the first 70 minutes, we created a lot of chances and we could have got a better victory today," he added.
"The last part of the game I think was a good lesson for us to know how we have to manage the game."
Cardiff manager Neil Warnock said his players must cut out their mistakes as they slipped to 16th stuck on 14 points.
"We set ourselves up to be difficult to break down and I can not legislate for individual errors," he said.
"We cannot keep playing like this every week and losing, we need to get results away from home."
(Reporting by Hardik Vyas in Bengaluru; Editing by Ian Chadband and Ken Ferris)
