Hull saw their hold on the second automatic promotion spot in the Championship cut to one point as nearest challengers Watford ran out 1-0 winners at the KC Stadium.
Troy Deeney grabbed the only goal of the match with a well-taken effort from the edge of the area after 41 minutes as the Hornets piled the pressure on Steve Bruce's Tigers, who now have the slimmest of leads to defend over the final six games of the season.
Only one other goal was scored across three other Championship encounters, that coming at the Reebok Stadium as Bolton clinched a 1-0 win Huddersfield.
Chris Eagles was the man on target after 58 minutes for the Trotters, who returned to winning ways after back-to-back losses to Ipswich and Charlton and are now six points off the play-off places.
The night's other matches ended in goalless draws. Brighton and Charlton drew a blank at the Amex Stadium as the hosts failed to leapfrog Nottingham Forest into fifth, while Middlesbrough were held to a stalemate by second-bottom Peterborough at the Riverside but climb a place to ninth.