Watford 2 Hull City 1
Aidy Boothroyd's decision to deploy his first team - which said as much about Watford's desperate need for a win as it did the desire to avoid a repetition of the last round when penalties were needed to defeat Accrington Stanley - had the desired effect as goals from Ashley Young and Tamas Priskin put the Hornets in control before Nick Barmby's overhead kick led to some late anxiety.
The Hornets boss couldn't have wished for a better start as his side took the lead after just two miuntes.
Hungarian striker Priskin was fouled by Damien Delaney 25 yards from goal and Young got the free-kick up and over the wall to beat Boaz Myhill, even though the keeper got a hand to the ball.
The Championship strugglers came back well from that setback though, with Jon Parkin seeing a well-struck volley blocked by Jordan Stewart and John Welsh shooting over the target from a good position on the edge of the Watford area.
Ben Foster also had to make a good save to deny Stuart Elliott, but as the first half progressed, Watford began to assert their superiority.
Danny Shittu headed a Young free-kick wide at the back post and Myhill twice thwarted Priskin, including a save from an improvised back-heeled flick to meet Hameur Bouazza's cross.
If Hull came out with hopes of turning the tie around, they shot themselves in the foot nine minutes after the restart.
A poor Ryan France header back across his own penalty area fell invitingly for Priskin and the young striker broke free to emphatically beat Myhill from 12 yards to net his first senior goal since moving to Vicarage Road in the summer.
Young and the impressive Darius Henderson then went close as Watford maintained their control on proceedings only to let it slip after 70 minutes following a double change by Parkinson.
Having introduced Darryl Duffy, the Hull manager then sent on Barmby and with his first touch the former England international superbly executed an overhead kick from eight yards out to hand his side a lifeline.
From being in command, nerves began to creep into the Hornets' play and there was an anxious moment when a mis-hit Foster clearance rebounded to Parkin, but the big striker sent his angled 30-yard chip narrowly wide.
Hull continued to push for the equaliser with substitute Mark Yeates directing his header straight at Foster, before the Hornets keeper had to dive full length to keep out Ian Ashbee's late piledriver.