Mileta Rajovic and Tom Dele-Bashiru spared Watford blushes as the Hornets edged to a 2-1 FA Cup third-round victory over Chesterfield.
Defeat was a cruel blow for the non-league side, who deserved at least a replay against their higher-placed opponents
The Championship side gave a first start to Rhys Healey, while Chesterfield made five changes – Liam Mandeville, Ryheem Sheckleford, Joe Quigley, Ollie Banks and goalkeeper Ryan Boot coming in for the National League leaders.
Watford almost took a fifth-minute lead when Yaser Asprilla intercepted a back pass from Branden Horton, but his effort was blocked by Sheckleford.
Backed by 3984 visiting supporters, Chesterfield were able to comfortably keep their EFL opponents at bay.
Indeed, they were able to create some pressure of their own, forcing a number of corners.
Yet they were almost undone on 24 minutes when Ismael Kone found space to bear down on goal – but his shot was saved by Boot.
The National League side then stunned their hosts on 27 minutes. A cross from the byline by Sheckleford found the head of Quigley, who directed a simple header into the net.
The goal visibly gave Chesterfield confidence, who started to move the ball around with authority, while Watford struggled to muster much of a meaningful response.
It could have been even better for the visitors less than 40 seconds after the restart, when keeper Daniel Bachmann had to save from Banks, following a move involving Sheckleford.
Watford started to get on the front foot to put their non-league opponents under pressure. However, their final delivery was lacking the quality needed to unlock the Chesterfield back line.
Chances for the hosts remained at a premium though, as the away side seemed content to soak up any advances.
Needing a drastic change in their fortunes, Watford made three substitutions – Giorgi Chakvetadze, Healey and Matheus Martins making way for Imran Louza, Rajovic and debutant Jorge Hurtado respectively.
It was one of the replacements in Rajovic that broke the Chesterfield resistance on 76 minutes, when he headed in a cross from Asprilla – to the clear relief of the majority of the Vicarage Road crowd.
The difference in the energy levels of both sides was apparent, as the Championship side looked to finish the game off while Chesterfield were looking to hang on.
Yet the non-league side could have won with seven minutes remaining, when sub Ryan Colclough headed over from less than six yards out following a header from Ash Palmer across the face of goal.
Boot was forced to palm away a fierce Dele-Bashiru effort with two minutes remaining.
But the keeper was beaten by Dele-Bashiru in the fourth minute of stoppage time to break Chesterfield Hearts.
