The 24-year-old was the Hornets' main attacking threat in the Premier League last term, scoring 10 goals and grabbing six assists as the club battled to avoid relegation.
Such was the level of his performances, Dennis will get a fresh opportunity to shine in the top flight with a £20million move to the City Ground on the cusp of completion, as revealed by Watford head coach Rob Edwards on Friday.
Speaking before the match, Edwards told Sky Sports: "It's progressing.
"I said in the media yesterday that everyone who we picked in the squad tonight would be fully focused and with us, and so that one's progressing."
He also revealed that a move to sign Keinan Davis on loan from Aston Villa was moving closer, saying: "That one's quite close and we're really pleased with it. We're onto the last bits of the medicals and we're hoping to welcome him in pretty soon."
Despite losing their star striker, the Hornets were able to come away with a crucial three points at Vicarage Road.
With the Clarets set to be one of Watford's closest rivals in the hunt for promotion this term, it was midfielder Tom Cleverley who gave the Hornets the lead with a well-taken effort just before the half-time interval.
Vincent Kompany's side dominated play in the second half and certainly had their chances to draw the game level, with Dan Bachmann pulling off a wonderful stop to deny Josh Brownhill.
Watford's task then become harder when Hassane Kamara was sent off with 10 minutes to go.
However Edwards' side managed to hold on for a valuable win that has seen them earn seven from a possible nine points since suffering the drop.