After a home loss to Leicester on Saturday, Chelsea bounced back with a well-deserved win at Vicarage Road. They remain 11 points behind league leaders Liverpool.
The match, however, was overshadowed by the injury suffered by Watford defender Christian Kabasele, who crashed into the goalpost early in the game. Despite appearing to suffer a rib injury following the collision, he tried to continue but ended up being carried out of the grounds on a stretcher while being given oxygen.
But Watford equalised moments before the break with a well-worked corner to Argentine midfielder Roberto Pereyra, whose superbly-timed volley from the edge of the box rocketed into the net for his sixth Premier League goal of season.
Hazard scored the winner from the spot early in the second half after being brought down by Foster.