Goals in each half from Troy Deeney and Joe Garner saw Watford pull away from the relegation zone with victory at fellow strugglers Millwall.
Debutant Alex Kacaniklic fed Deeney to fire the visitors ahead with a neat finish from the edge of the area.
Watford keeper Scott Loach saved from Liam Trotter before Garner slotted home after Deeney was denied by David Forde.
Trotter's header hit a post and Loach saved a Darius Henderson penalty after John Marquis was fouled by the keeper.
The result ended a run of three successive league defeats for Watford, while Millwall are now just one place above the relegation zone.