Robert Koren's late strike gave Hull victory and condemned Watford to their fourth successive Championship defeat.
The Hornets twice took the lead, firstly when Hull defender James Chester headed into his own net.
Matty Fryatt equalised from close range before Chris Iwelumo's header restored Watford's advantage.
Aaron Mclean levelled things again with a neat finish from 12 yards, and Koren stole the points when he lashed into the bottom corner.
It was a resilient display from the home side, who twice came from behind to extend their unbeaten league run to eight games.
The visitors took the lead just after the half-hour mark with the first real chance of the match as Chester diverted Mark Yeates' cross past Adriano Basso.
The home side were back level shortly after half time when Fryatt pounced to convert Tom Cairney's cross from six yards out.
Marvin Sordell went close for the visitors before Iwelumo restored the advantage by nodding in from close range - his first goal for Watford.
But Hull were level again 10 minutes later when Aaron Mclean fired into the bottom corner, and the turnaround was complete four minutes into injury time when Koren received the ball 25 yards and struck a fine shot into the bottom corner.