Sam Clucas sealed a memorable win – despite Hull being harshly reduced to ten men by a controversial sending off.
The midfielder volleyed home from 25 yards to give Hull the points in a fantastic, against-the-odds home win.
Hull were livid after Oumar Niasse was dismissed for a foul on M’Baye Niang after 25 minutes.
But second half goals from Lazar Markovic and Clucas stunned sleepy Watford.
Here are five things we learned...
Marco Silva, miracle worker
Since he took over in January Hull have won seven out of eight home games in all competitions.
That’s included 19 points from 21 in the league, completely reviving their survival hopes.
This was the bravest of them all – with ten men for an hour. He’s got his players and the Kcom crowd believing.
It is 41 games in the league at home since Silva experienced defeat at three clubs.
The red card rage for Hull
The game was ambling along without incident when ref Robert Madley stunned everyone and pulled out a red card.
M’Baye Niang was caught on the shin by Oumar Niasse who went down with a scream audible in the press box.
Madley showed a straight red, but in reality it was just a mistimed tackle, and maybe, a yellow.
Not surprisingly the home crowd were furious. It ruined Hull’s chances of a win, and the game.
But Lazar Markovic sets up a ten man win
Hull’s chances looked terrible after they went a man down, but on te hour they were one up.
Watford looked lethargic, sent too many men up for a corner and were caught by a break-away.
Kamil Grozicky sped down the right wing and crossed for Markovic to head onto the bar, bouncing down onto the line.
The striker followed up by crashing the ball home. Remarkable.
As was Sam Clucas’s second – a sweetly struck long range volley.
Can Hull stay up?
At 3.15pm they dropped into the bottom three again when Swansea took the lead, but turned the day around.
Their away form must improve if they want to survive, starting at Southampton next week, but this is more progress.
They have Sunderland at home the week after, which could mean points.
It will go to the last game, but Hull are fighting for their lives and it is impressive.
No away goal in league since January for Watford
They may be sitting safely in mid table with the job largely done, but Watford can’t score on their travels.
Sebastian Prodl had a header brilliantly saved and Daryl Janmaat a volley blocked.
Troy Deeney had a chance from 6 yards but somehow hit the keepers foot.
They were in second gear here, not sharp enough to capitalise.