Two first-half goals in quick succession from Adrian Mariappa and Henri Lansbury put the Hornets firmly in the driving seat, although Marcus Tudgay's header on the stroke of half-time gave the visitors hope.
But the Owls were a poor second best for most of the night and it showed after the break as the home side completed a great night's work through Jon Harley and Lansbury's second.
John Eustace, on as an early replacement for the injured Ross Jenkins, set up the first with his first touch when he drove the ball back across the penalty area following a Watford corner and Mariappa was lurking unmarked in the six-yard box to tap home in the 20th home.
Watford doubled their advantage six minutes later with a classy second.
Lansbury exchanged passes with Tom Cleverley on the edge of the penalty area before darting in between two defenders with a quick change of feet and he then switched his weight again onto his right foot to beat Lee Grant at his near post.
But Wednesday gained a foothold in the contest in first-half injury-time when a long Tommy Spurr throw found Tudgay in the area to head past Scott Loach from close range.
The home side re-established their two-goal cushion in the 54th minute.
Again Lansbury was involved, this time keeping an attack going following a corner, picking the ball up on the right and laying it inside to Harley, who picked his spot superbly with a left-foot blast across Grant.
Watford 's fourth came seven minutes later and again it oozed class.
Cleverley was the orchestrator this time, picking up the ball on the edge of the box and running and attacking the right side of the area as he toyed with the bemused Wednesday defenders before laying the ball across for Lansbury to side-foot home his second.