For the first game between the rival clubs in four years, manager Joe Kinnear selected Carl Emberson in goal as the only change from the goalless draw at Griffin Park four days earlier, after Charlton boss Alan Curbishley refused permission for on-loan Ben Roberts to play in the competition.
Out-of-favour striker Tony Thorpe was dropped from the matchday squad completely, with Carl Griffiths and Andrew Fotiadis coming onto the bench to make up the 16.
Watford, who had made an unbeaten start to their home league campaign, winning three and drawing one, included ex-Hatters Alec Chamberlain and Sean Dyche in their side.
WATFORD: Chamberlain, Ardley, P Robinson, Cox, Dyche, Hyde, Smith, Glass, Doyley, Foley, Hand. Subs not used: Vernazza, McNamee, Ifill, Norville, Lee (GK).
TOWN: Emberson, Boyce, Perrett, Bayliss, Davis, Brkovic, Nicholls, Spring, Hughes, Howard, Crowe. Subs not used: Neilson, Griffiths, Robinson, Coyne, Fotiadis.
REFEREE: Peter Walton (Northants)