Republic of Ireland midfielder Hendrick outjumped Jose Holebas to nod the Clarets in front seven minutes before the interval, before Keane crashed home a second header past Heurelho Gomes to seal the points.
The win hauls the Clarets to 13th in the table, level on points with Monday night’s opponents, and a result which prevents the Hornets from racking up a third consecutive victory in the league.
Change in formation is vindicated
Manager Sean Dyche kept faith with the five-man midfield that had struggled to restrain Leicester City last weekend, with Sam Vokes replacing the suspended Andre Gray and Johann Berg Gudmundsson coming in for Scott Arfield.
And Dyche’s persistence was rewarded with a high-intensity, industrious display from his side, who buzzed with creativity from the off. It was they who looked the brighter in the opening 10 minutes, and George Boyd tried to capitalise with only a smart save from Gomes denying the winger an early goal.
The pressure continued to mount on Watford, and hearts were in mouths when Vokes rose for a header, but a vital deflection turned the ball wide as the Hornets struggled to stem the flow from their hosts. Gudmundsson’s drive and left-footed effort also went wide, with only a goal missing from Burnley’s early attacking endeavour.
But eventually, Watford relented and conceded the opening goal of the night. Midfielder Steven Defour’s corner from the right was met by the towering Hendrick, who showed superb accuracy to steer the ball back across goal and into the far corner to give the Clarets the lead.
By contrast, the Hornets created little in terms of attacking opportunities in the opening 45 minutes, with Holebas’ volley from the edge of the area repelled by a resolute Burnley rear-guard in what proved to be a rare sighting of goal for the visitors.
Defour proves his worth
Watford boss Walter Mazzarri would have demanded more from his charges after the break and, although his side flickered into life for the opening five minutes of the second half, they found themselves 2-0 down moments later.
Once more, Defour was the architect and, for all his tirless work off the ball, the Belgian is just as useful on it. This time, his wicked in-swinging cross from the left was met by Keane’s thumping header, who wheeled away from a heap of bodies to celebrate a precious goal for his side.
Despite the 2-0 cushion, some Burnley fans may have urged for caution, particularly when Watford had found themselves 2-0 down at West Ham’s London Stadium just over a fortnight ago, and had rallied back on that occasion to run out 4-2 winners.
However, they could not convert fleeting signs of life into anything more significant, and very nearly conceded a third when Vokes found himself one-on-one with Gomes, but the Brazilian goalkeeper marshalled the Burnley forward away from goal, of which his scuffed effort went wide.
A win expertly held out for
With time running out, Watford began to have more of the ball but, for all their possession, there was little in terms of penetration. Substitute Isaac Success saw a rare venture forward end disappointingly; his low ball across the box flashed agonisingly wide of the far post before Valon Behrami saw a late volley fly just wide through a crowd of Claret players.
Success had the last notable moment of the game, firing over the angle from Troy Deeney’s pass, but it was to be a fruitless night for their side as Dyche's men successfully negated the threat of their visitors.