Luton's James Collins thumped a shot against the bar moments before Watford opened the scoring
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.
Vladimir Ivic's Hornets are still yet to concede in the league this season and have seven points from three games, bouncing back from their surprise midweek Carabao Cup defeat against League Two side Newport.
Defeat for Luton sees them drop their first points of the campaign - off the back of a 3-0 cup loss to Manchester United on Tuesday.
Watford gave a first start of the season to winger Ismaila Sarr - who has been linked with Liverpool and, more recently, Aston Villa this summer - while talisman Troy Deeney came off the bench in the closing stages for his first appearance since their relegation from the Premier League.
The Hatters really ought to have led when Collins could not keep his shot down from six yards from Harry Cornick's cross, and Pedro punished them - albeit with the help of a deflection off defender Sonny Bradley on its way in.
Republic of Ireland striker Collins also had Luton's best second-half opportunity, firing over when two team-mates were arguably better placed.
It means Watford are unbeaten in 10 league meetings with their Bedfordshire foes and have kept clean sheets in their opening three league games for the first time since the 1988-89 season.
Watford head coach Vladimir Ivic:
"You recognise quality players and sure Joao Pedro has quality. In the system that we play, he brings a lot of different things.
"We started this game much better than our other four games. We deserved this victory. We were the better team from the beginning until the end. Luton created just one chance.
"We created four or five chances and we could have scored more goals but OK, game by game I believe that our performance will be better. I said a lot of times that we are not at 100% of our ability."
Luton head coach Nathan Jones:
"A real lacklustre game, the most lacklustre derby you have ever seen. I don't think you would realise it was a derby. We were flat.
"The game changed in two minutes and that was the difference between the two teams. If we had scored we would have got a point at minimum because they probably wouldn't have scored their goal.
"But I am just flabbergasted by the performance. I did not see that coming. I thought at least we would be right at it. If there had been fans in the stadium they would have demanded more."
