Joao Pedro's goal earned Watford victory over Luton in the first meeting between the rivals in 14 years as the Hornets maintained their unbeaten Championship start.
The Brazilian forward, on his 19th birthday, converted Ken Sema's low cross from close range less than a minute after a James Collins shot struck the underside of the bar for the visitors.
Luton could not create any more clear openings and would have lost by a wider margin had keeper Simon Sluga not saved brilliantly from Watford midfielders James Garner and Tom Dele-Bashiru.
The lack of fans at Vicarage Road took away much of the intensity from what was a hotly anticipated match.