Adam Le Fondre's 12th minute tap in was the only goal in a difficult fixture at Vicarage Rd.
City withstood a Watford attack that looked sure to get themselves back into the game but as time wore on the belief fell away from the home side and Russell Slade can be grateful to finally see an away victory achieved.
City lost Matt Connolly and more worrying Anthony Pilkington to injury during the game, the latter suffering a pulled hamstring as he unleashed a rare shot at the Watford goal.
Le Fondre won't have scored an easier goal. Kenwynne Jones, in for Macheda as the only change from the side that beat Reading last week, beat Gomes in the air allowing Le Fondre the easiest of chances to put City in front.
City made a decent effort during the first half and despite Watford looking the more dangerous City were good value for their lead. Le Fondre saw another effort saved while at the back City defended well and restricted Watford to half chances.
Before the game Watford officially opened The Graham Taylor Stand, with Taylor himself the special guest along with several of the players and staff from Taylor's era. But like the 14,500 home supporters they would go away disappointed.
The second half started with full on Watford pressure a goal seemed inevitable but City held out, rode their luck, dug deep and eventually frustrated the home side into submission. Cardiff nearly caught Watford on the break on more than one occasion but when the referee finally blew the whistle after 5 mins of added time the ball was deep in the Watford half. Graham Taylor would not have liked that.
The boss is delivering promotion form from his eight games in charge so far. Long may it continue.
Watford: Gomes; Angella, Ekstrand, Bassong; Paredes (Forestieri 66), Munari, Tozser, Abdi (Guedioura 66), Anya; Deeney, Vydra. Not used: Gilmartin, Doyley, Cathcart, Pudil, Dyer.
Cardiff City: Marshall; Brayford, Morrison, Turner, Connolly (Fabio 51); Pilkington, Gunnarsson (Adeyemi 73), Whittingham, Noone (Ralls 70); Jones, Le Fondre. Not used: Moore, Macheda, Moller Daehli, Maynard.
Attendance: 15,668 (1,035 away).
Referee: Philip Gibbs.