Watford completely dominated Barnsley to run out 4-1 winners in the Championship clash at Vicarage Road this afternoon.
After 10 minutes, the Hornets took the lead when Deeney headed in Mark Yeates's corner at the back post.
The home side came close again through another Yeates set piece, but the chance was missed.
Two corners from Barnsley caused the Watford defence problems on 20 minutes, forcing Manuel Almunia into an impressive save.
Fernando Forestieri tested Luke Steele with a strong strike and the goalkeeper stood up well to deny the forward.
Deeney almost grabbed a second goal on 28 minutes, but his effort was well blocked by the defence.
Marco Cassetti came close from the resulting corner, hitting the top of the crossbar with his near-post header.
Forestieri could have doubled Watford's lead after a defensive error left him free, but the Italian wasted the chance.
Watford doubled their lead after 59 minutes when Deeney turned provider, playing in Yeates, who scored from a tight angle.
Deeney got his second and Watford's third after Forestieri's quick free kick allowed him to rifle home.
Deeney almost claimed a hat-trick, but he fired his shot straight at Steele after a defensive error from Barnsley.
Watford were awarded a penalty after Matej Vydra was hauled down. The Czech then stepped up to make it 4-0.
Barnsley grabbed a late consolation through Marcus Tudgay to make it 4-1 before the referee brought the game to an end.
