Burnley scored twice in the final seven minutes to complete a dramatic comeback that pulled them five points clear of the Premier League relegation zone and left hosts Watford on the brink of relegation.
Jack Cork's diving header from Charlie Taylor's left-wing cross cancelled out James Tarkowski's early own goal, before Josh Brownhill found the bottom corner from the edge of the box to spark jubilant scenes among the travelling fans and in the away dugout at Vicarage Road.
Watford had taken a deserved early lead when Juraj Kucka's fierce effort struck the crossbar before rebounding off the unfortunate Tarkowski and into the unguarded net.
The Hornets carried the greater threat in the first half, Kiko Femenia striking the near post from an inswinging corner and Joao Pedro blazing over the crossbar after escaping the Clarets defence.
Aaron Lennon and Ashley Barnes forced fine saves out of Ben Foster in the second half, but there was little the veteran goalkeeper could do about either of the visitors' late goals, which came in the space of three minutes.
The Hornets' 11th consecutive home defeat leaves them 12 points adrift of Burnley and Leeds - who play Manchester City later on Saturday - with only four games remaining.
Clarets caretaker boss Mike Jackson said: "We are delighted with the result and the second-half performance, first half we were not where we needed to be. We knew at 1-0 the crowd might get a bit edgy and if we stick with it and get more possession we could get a back in the game
"I don't think we started the game well enough, the tempo we started at, we didn't get to those levels we have done recently - we improved the quality with the ball, at this stage of the season you just have to find ways of winning games.
"These games are so emotionally charged with what is at stake, credit to them for finding a way to win the game.
"We just reminded the group who they are, there was a lot of good work before, so for me it is reminding this group who they are and making sure they deliver on the standards they are capable of.
"When I get on the train later on and maybe have a glass of wine, I might take a breather and enjoy it."
