Cardiff City may have almost secured the title, but the Championship's second automatic promotion place remains wide open after Gianfranco Zola's Watford put their recent poor form behind them to secure a vital three points on the ground of their closest rivals.
It was a fine performance by the Hornets, whose first-half dominance was capped by Troy Deeney's fine 41st-minute strike, and with a defence well marshalled by Joel Ekstrand and Marco Cassetti they always looked in control.
"A lot of brains and a lot of passion went into that performance and we got the reward," said Zola. "We played very well in the first half and we fought very hard in the second. If we had lost Hull would have gone seven points clear and been very difficult to catch, but this team has never let me down in important games."
After a cagey opening Watford took control, and the chances began to come before Deeney's 20-yard drive in the run up to half time gave City goalkeeper David Stockdale no chance.
Hull had yet to get an effort on target, but they did receive some encouragement when Watford goalkeeper Jonathan Bond had to get down quickly to block George Boyd's effort.
The home team's best period came in the 10 minutes after the break, when Bond – still only 19 – made fine saves from Jay Simpson and Robert Koren, but Watford remained dangerous on the counter-attack.
City's manager, Steve Bruce, switched things around, trying several different combinations up front, but his side continued to find it hard to create opportunities.
"A fair result would have been a draw, but we couldn't get the breakthrough," said Bruce. "It would have been nice to have been sitting seven points clear, but I've been at this club eight months now and we never do things easy. We're still in second, it's still in our hands, and one thing we have done this season is bounce back."
Hull City (3-5-2): Stockdale: Hobbs (Proschwitz, 77), Faye, Chester: El-Mohamady, Koren, Bruce (Quinn, 68), Boyd, Brady; Simpson, Gedo (Evans, 69) Substitutes not used Jakupovic, Rosenior, Cairney, Fathi.
Watford (3-5-2): Bond: Ekstrand, Hall (Doyley, 26), Briggs (Pudil, 55); Cassetti, Abdi, Battochio, Chalobah, Anya; Deeney, Vydra (Buaben, 83). Substitutes not used Bonham, Yeates, Geijo, Forestieri.
Referee R Madley (West Yorkshire).
Eagles gives Terriers blues
Chris Eagles scored the only goal of the game at the Reebok Stadium to help Bolton to a 1-0 win over Huddersfield - a result manager Dougie Freedman called "a major victory" for his play-off chasing side. The midfielder's goal just before the hour gave Bolton a sixth straight home win and left Huddersfield in the relegation zone. Brighton's were held 0-0 by Charlton at the Amex Stadium, while Middlesbrough's match with Peterborough also ended goalless.