Goals by Andy Gray and Joey Gudjonsson were enough to upset top-of-the-table Watford and give Owen Coyle his first win as Burnley boss.
Marlon King wasted a good early chance for Watford but Burnley hit the bar through Chris McCann's header before Gray steered home a Wade Elliott cross.
Gudjonsson's fine solo goal made it 2-0 before Danny Shittu met King's lay-off to pull one back for the Hornets.
Watford piled forward in search of an equaliser but Burnley held on to win.
Watford manager Aidy Boothroyd:
"It was an awful spectacle, it was absolutely shocking.
"When we lost at Barnsley on Saturday, there were some aspects of the game I could be pleased with but not tonight.
"We were lacklustre and it was like looking at a team of clones. It was a sub-standard performance from minute one and it didn't get any better."
Burnley boss Owen Coyle:
"There's a few more grey hairs there tonight but I have to say that we merited all three points.
"I asked them to be brave and to keep passing the ball and in the end I thought we scored two very good goals.
"When Watford scored they threw everything at us including the kitchen sink but we stayed strong as a team."
Watford: Poom, Doyley, Shittu, DeMerit, Stewart (Francis 75), Smith, Mahon (Ellington 80), Williamson, Kabba, King, Darius Henderson (Priskin 74).
Subs Not Used: Lee, Jackson.
Goals: Shittu 86.
Burnley: Kiraly, Alexander, Carlisle, Unsworth, Harley, Elliott, McCann, Mahon, Lafferty (Gudjonsson 46), Gray (Akinbiyi 87), Blake (Jones 83).
Subs Not Used: Jensen, James O'Connor.
Goals: Gray 58, Gudjonsson 80.
Ref: Kevin Friend (Leicestershire).