Championship wrap: Deeney winner spurs on Watford
Watford moved to within a point of second place after edging promotion rivals Hull 1-0, while Bolton heaped more misery on Huddersfield.
A solitary goal from Troy Deeney proved the difference for the visitors against their second-placed opponents at KC Stadium on Tuesday.
Four points separated second and third spot before the kick-off, with Hull winning six of their past nine league outings, while Watford had failed to win in three attempts.
But Gianfranco Zola's men ended that run courtesy of Deeney's 41st-minute strike that found the top corner from the edge of the area.
The result narrows the gap between the two sides, with Watford just one point adrift of the automatic promotion position.
At the Reebok Stadium, Bolton snapped a two-game losing run by claiming a 1-0 win over lowly Huddersfield.
Former Manchester United midfielder Chris Eagles made the decisive breakthrough three minutes before the hour, his second goal in four games.
Bolton, who have now won six successive home fixtures, leapfrog Derby into eighth and close to within three points of the top six.
Huddersfield, meanwhile, remain in the relegation zone on the back of their third defeat in five games.
In Tuesday's two other fixtures, Middlesbrough's winless run extended to five matches after being held to a goalless draw at home to relegation-threatened Peterborough, while Brighton and Charlton failed to find the net in their meeting at the American Express Community Stadium.