A brace either side of half time from Curtis Davies and a late goal courtesy of Chris Burke gave the Blues what turned out to be a fairly comfortable win, lifting them to sixth in the Championship.
Both teams began the match tentatively, with neither goalkeeper tested in the opening exchanges. Indeed, it wasn't until the 17th minute that there was a sight of goal, and it fell to the home side.
A high cross from Burke almost caught Watford keeper Scott Loach off guard, and his palmed clearance fell to the feet of Marlon King but the former Watford man couldn't take advantage.
The much-needed breakthrough finally came in the 35th minute after Jordon Mutch's corner was cleared before being laid back to Keith Fahey, who in turn found Davies with a cross and the centre-back made no mistake with his header.
The Blues suffered a blow early in the second half when King was forced to come off with a suspected groin strain, and seconds later the visitors had their first real chance of the game, a shot from distance from Marvin Sordell forcing Boaz Myhill into a low save.
Despite Watford's continued pressure, they weren't creating any goalscoring chances, and they were punished on the hour mark through Davies's second.
This one came directly from Mutch's corner as the defender powered home his third goal in the last two games.
The home side were on the offensive immediately after their second too, Fahey causing Nyron Nosworthy to nervously head his cross behind.
The Blues were then denied a penalty when Zigic claimed that he was brought down in the box, but his appeal was swiftly turned down by the referee, much to the dismay of the home fans.
They eventually found a third goal, however, when a clever flick from Rooney was well saved by Loach, only for Burke to hammer the follow up into the back of the Watford goal.
Redmond almost made it 4-0 late on, only to be denied by a good save from Loach.