Davies hadn't played since the defeat to Cardiff on October 18 because of an ankle problem, with Pearson having returned from a similar length injury against Sheffield Wednesday last week only to miss the midweek defeat to Blackburn.
The others to come into the side were Jordan Storey, Brad Potts and Sean Maguire, all having come off the bench in the latter stages of the Blackburn game.
With no full-backs available, North End manager Neil switched to a 3-5-2 system with Tom Barkhuizen and Scott Sinclair in the wing-back roles.
Alan Browne and Joe Rafferty missed out through one-match suspensions, with Darnell Fisher starting a three-game ban.
Paul Huntington and Ryan Ledson dropped down to the bench which had youngsters Adam O'Reilly, Jack Baxter, Lewis Coulton and Jacob Holland-Wilkinson on it.
Watford: Foster, Ngakia, Kabasele, Cathcart, Femenia, Sarr, Chalobah, Garner, Quina, Deeney, Gray. Subs: Troost-Ekong, Wilmot, Pedron, Percia, Sierralta, Navarro, Crichlow, Phillips, Bachmann.
PNE: Rudd, Storey, Bauer, Davies, Barkhuizen, Pearson, Johnson, Potts, Sinclair, Maguire, Riis. Subs: Bayliss, Ledson, Stockley, Huntington, Holland-Wilkinson, Baxter, O'Reilly, Coulton, Ripley.
Refereee: Jarred Gillett
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