After 20 minutes, though, Quina made no mistake. The 20-year-old picked the ball up from deep and, with Davinson Sánchez backing off, ran to within 25 yards of goal and fired a swerving drive past Joe Hart.
Spurs came close to equalising immediately through Son but Daniel Bachmann got down well to save the forward’s low effort from a wide position.
The Hornets then doubled their lead shortly before half-time, as Gray smashed a penalty past Hart after Dele-Bashiru was pulled down in the area.
Gray almost scored again soon after the break, latching onto an incisive through-pass by Quina. Under pressure from two defenders, the striker’s effort went wide of the post.
As the game wore on José Mourinho’s side pushed forwards and Watford’s defensive resolve was tested, but Nathaniel Chalobah brilliantly blocked a Lamela strike before Bachmann saved from the Argentine.