Jim Magilton was denied the services of a number of first-team players through injury and suspension, but the Tractor Boys boss must have been delighted with how his patched up side went about the task in hand.
They hit the woodwork twice, were the better side in the opening period and more than contributed to what became an end-to-end second half, but the fact they had to play the entire second 45 minutes with only ten men after debutant George O'Callaghan stupidly got himself sent off at the end of the opening period probably told in the end.
Ipswich were light on numbers at the back when the Hornets strung together a flowing end-to-end move that created the winner and belied what was otherwise an indifferent display by Aidy Boothroyd's men, but the fact they have strung together back-to-back wins for only the second time this season will put them in very good heart for this week's massive relegation clash with Wigan Athletic.
The home side started well enough, with Steve Kabba seeing a first-time shot deflected before the January capture from Sheffield United somehow failed to beat Lewis Price from close range, after Darius Henderson had headed a Dan Shittu flick-on in his direction.
Slowly though, Ipswich established a foothold in the contest and they almost took the lead with a bolt from the boot of Sylvain Legwinski that thundered back off the crossbar from 25 yards and left Watford keeper Richard Lee, who appeared to think the drive was going over, a relieved man.
The lively Danny Haynes and O'Callaghan also had decent first-half efforts as the visitors looked the more cohesive side, only for the latter to ruin what had been a promising debut by stamping on Shittu in first-half injury-time and referee Steve Bennett had no hesitation in producing a straight red card.
Ipswich started the second half as they had played for the majority of the first, with Haynes forcing Lee into a smart save moments after the restart, but Watford thought they had taken the lead when Matt Richards' clearance to a Henderson header from a corner appeared to have been made from behind the goal-line.
The officials though, were unmoved, but it was another example that will further boost the calls for goal-line technology.
Ipswich survived another let-off when Kabba failed to convert a Henderson flick-on from close range, but it was the Watford goal's turn to lead a charmed life when centre-half Chris Casement ventured forward to let fly with a blistering right-footed drive that beat Lee, but bounced down off the underside of the bar.
Watford increasingly made their numerical advantage tell as the minutes elapsed, but Ipswich looked like they would take the tie back to Portman Road until three minutes from time.
A good ball out of defence down the right flank by the impressive Adrian Mariappa was superbly touched into the path of Tommy Smith by Kabba and the Hornets winger went streaking away before cutting the ball back towards Henderson.
He cleverly left it for Francis behind him and the central midfielder didn't need a second invitation and calmly side-footed a left-footed finish past Price to book his side's place in the last eight.