With the scores level at 0-0 after extra time, the Hornets won the penalty shoot-out 4-1 to set up a quarter final home clash against Tottenham Hotspur.
Watford: Kirk; Osborne, Mariappa, Homand, Parkes; Campana (Frost 105), Bangura (Matthews 67), Gilligan; Diagouraga; Grant. Subs not used: Bardle, McCoy, Cader.
Middlebrough: Knight; Burgess, Bates, Wheater, Hines; Clough, Cattermole, Grounds, Johnson; Craddock, Kennedy. Subs not used: Lemaire, Robter (GK), Walker, Robson, Williams.