An 86th-minute goal from Ashley Fletcher on his full debut ensured Watford made it through to the Carabao Cup third round at the expensive of Premier League rivals Crystal Palace.
The tie at Vicarage Road seemed destined for a penalty shoot-out until the summer signing tapped home at the back post to earn the Hornets a 1-0 victory which leaves new Eagles boss Patrick Vieira winless and without a goal after three matches in charge.
While the visitors went strong, with Wilfried Zaha and Conor Gallagher in from the off, Watford mixed up their starting XI with three full debuts handed out and Ben Foster in goal as one of the seven changes.
It was therefore perhaps little surprise Palace looked the more cohesive unit and the recalled Jean-Philippe Mateta should have opened the scoring in the first half.
The Mainz loanee tested Foster for the first time in the 13th minute from a tight angle, creating the opportunity from what seemed a lost cause, and four minutes later was presented with a better chance but headed onto Watford defender William Troost-Ekong from close range.
Mateta had another effort at the end of the half but Watford's captain for the night tipped over with ease before James Tomkins headed wide, with the Hornets' only attempt of note a curler from Imran Louza which was off target.
After the break the hosts came out a different side and Troost-Ekong forced Jack Butland, deputising for Vicente Guaita, into a superb diving save early into the second period before Cucho Hernandez and Fletcher had shots but they failed to test the Eagles custodian.
Having weathered the storm, Palace got back into their stride and Christian Benteke was denied with quarter of an hour left before Fletcher steered home Hernandez's cross to secure a narrow triumph for the hosts.
