Goals from Ashley Young, a Hameur Bouazza penalty and Dominic Blizzard ensured last season's semi-finalists where in complete command by shortly after half time, although the visitors did net a scarcely deserved consolation through Chris Palmer.
Hornets boss Adrian Boothroyd used the match to rest many of his first-choice line-up, but the youngsters he chose to play rose to the challenge in admirable fashion, causing the struggling Magpies defence countless problems with their free-flowing attacking football.
Watford set up their stall from the opening whistle and it was no surprise when they took the lead after 12 minutes. Lively left-winger Anthony McNamee delivered a fine cross from the left and the excellent Young pulled clear at the far post to head home a straightforward opportunity to register his third goal of the season.
The home side continued to turn the screw with Bouazza heading over a good opportunity following Young's corner and Blizzard narrowly failing to connect with a Young cross after some delightful build -up play that also involved Matthew Spring.
But Watford did make their next opportunity count, although it was gift-wrapped for them when Julien Baudet fouled Young in the penalty area and Bouazza made no mistake from 12 yards.
The Hornets were on Easy Street soon after the restart when Blizzard was presented with an easy third after Kevin Pilkington could only push another excellent Young delivery back into the middle of the penalty area.
County finally mustered their first goal attempt of the evening just before the hour, and this resulted in an improvement to their performance, culminating in them scoring with their first shot on target in the 75th minute.
David Pipe dispossessed Adrian Mariappa and, with the Hornets defence pushed upfield, the ball ran through to Palmer who advanced before calmly beating Alec Chamberlain with a low drive.