Luton Town boss Rob Edwards masterminded victory over his former side Watford as the promotion-chasing Hatters kept the pressure on the Championship's top two in a high-octane derby at a sellout Kenilworth Road.
Gabriel Osho's low first-half strike opened the scoring for the hosts - who had won four of their previous six matches 1-0.
Watford, who failed to register an attempt on target in the first half, improved after the interval and went close through a Jeremy Ngakia header.
But a poor clearance allowed Allan Campbell to smash in an injury-time second for the hosts, who are now unbeaten in seven games.