At a time when the Hornets sit in 10th position in the Championship standings, their opponents occupy top spot in the National League table.
Match preview
Ahead of the Christmas and New Year period, Watford looked well set to build on their recent good form and push hard to sit in a playoff spot come the end of the calendar year.
Instead, just two points have been collected from games against Bristol City, Stoke City and Plymouth Argyle, representing the first time that Valerien Ismael's side had gone three fixtures without success since the start of October.
As a result, Watford sit four points adrift of the top six, still very much in contention but aware that their recent slump marks a missed opportunity.
Three aways game in the Championship in succession follow this contest, and Ismael will want his players to regain some belief ahead of some time on the road.
Chesterfield will be making the trip to Vicarage Road for the first time since 1997, when they succumbed to a 2-1 defeat in the old Division 2.
Watford are playing their first game in this year's FA Cup, but Chesterfield have already come through three ties to book their place in the last 64.
Scoring five goals in a rout against Kettering Town was notable in itself, yet it was not in comparison to 1-0 successes over each of Portsmouth and Leyton Orient in rounds one and two respectively.
Paul Cook's side have remarkably won 21 of their last 24 games in all competitions, albeit one of their two defeats coming away at Solihull Moors on Boxing Day.
The Spireites played Championship opposition at this stage last season - going down to West Bromwich Albion in a replay - but that experience may stand them in good stead here.
Watford form (all competitions):
L
W
W
L
D
D
Chesterfield FA Cup form:
Chesterfield form (all competitions):
W
W
W
W
L
W
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Team News
Ismael is expected to make several changes to his Watford XI, including handing a first start to goalkeeper Daniel Bachmann since November 25.
Imran Louza, Yaser Asprilla and Rhys Healey will also hope to be included, while Francisco Sierralta may return at centre-back or in a defensive-midfield role.
Cook is likely to make fewer alterations to his Chesterfield XI as they bid to cause one of the upsets of the third round.
Although Chesterfield came from 2-0 down to beat Solihull Moors 3-2 on New Year's Day, all of the substitutions came after the revival.
That could mean that the likes of Ollie Banks - who scored in the fourth qualifying round against Kettering - and Liam Mandeville - who has five National League strikes this season - will remain among the replacements.
Watford possible starting lineup:
Bachmann; Andrews, Porteous, Hoedt, Morris; Louza, Sierralta, Kone; Asprilla, Healey, Ince
Chesterfield possible starting lineup:
Tyrer; King, Palmer, Freckleton, Horton; Oldaker, Naylor; Colclough, Jacobs, Dobra; Grigg
We say: Watford 3-0 Chesterfield
While this is something of a free hit for Chesterfield, they will also want to do themselves justice. Nevertheless, facing Watford on away territory is a big step up, and we anticipate that the Hornets will come through with a comfortable win.