Two first-half goals from midfielder Matthew Spring, taking his tally to eight for the season, put the Hornets in total control by the interval, and their rise up to third in the table was assured with further strikes from Marlon King and Ashley Young.
Sub Luke Rodgers did net a late consolation for the visitors but they were well beaten and Watford had plenty of other opportunities to have increased their margin of victory.
However it might have been a different story had Crewe managed to capitalise on the first clear cut opportunity of the match, a Kenny Lunt pass sent Steve Jones racing clear into the Watford area and he rounded Jordan Stewart before placing a shot beyond veteran keeper Alec Chamberlain, who was deputising for the injured Ben Foster.
However, Spring appeared out of nowhere to clear the ball against the crossbar to prevent a certain goal.
And soon afterwards the 26-year-old midfielder turned from goal saver to scorer, latching on to a pass from Darius Henderson and driving forward before striking a 30-yard shot beyond keeper Ross Turnbull.
It didn't take long for Spring to double his tally for the afternoon, this time sliding the ball through a crowded goalmouth after Turnbull had excelled to deny Henderson and Lloyd Doyley completely mishit the follow-up.
The Crewe keeper was replaced by Stuart Tomlinson at half-time, but within 12 minutes of the restart he was also picking the ball out of his net as Chris Eagles' flick-on found King in the inside right channel with his back to goal.
He showed good strength to hold off a defender before spinning and firing a low right-footed drive across Tomlinson and into the far corner for his 13th goal of the campaign.
A real rout looked on the cards when Watford scored the fourth on the hour, Young being in the right place in the six-yard box to divert home a low Eagles cross.
But although the home side had other chances to increase their lead it was Crewe who scored the game's only other goal when a Billy Jones cross presented Rodgers with a straightforward finish.