Erik Lamela put us ahead in the 17th minute but Watford drew level through Odion Ighalo shortly before half-time.
The hosts were then reduced to 10 men after Nathan Ake was dismissed for a foul on Lamela, but they still put us under a fair amount of pressure in the closing stages before Heung-Min Son popped up with a 90th-minute winner for us.
Watford (4-4-2): Gomes, Anya, Cathcart, Britos (Prodl 60), Ake; Abdi (Behrami 45), Watson, Capoue, Jurado (Nyom 68); Ighalo, Deeney (c). Substitutes (not used): Arlakauskis, Guedioura, Holebas, Diamanti.
Spurs (3-4-2-1) Lloris (c), Alderweireld, Dier, Vertonghen; Trippier, Dembele (Eriksen 45), Carroll (Son 68), Rose; Lamela, Alli (Chadli 81); Kane. Substitutes (not used): Vorm, Davies Walker, Mason.
Goals: Watford – Ighalo 42; Spurs – Lamela 17, Son 90.
Yellow cards: Watford – Britos 50, Behrami 58, Deeney 62, Ighalo 65; Spurs - Alli 5, Alderweireld 80.
Red card: Watford – Ake 62.
Referee: Anthony Taylor.