Match ends, Watford 1, Derby County 2.
Derby went clear at the top of the Championship after Craig Bryson's impressive strike from outside the area saw them win at Watford.
Jordan Ibe put the Rams ahead six minutes before half-time when he found the net from 20 yards.
The hosts dominated much of the second half and Gianni Munari struck a deserved equaliser from close range.
But Bryson secured the win for Steve McLaren's side when he fired high into Jonathan Bond's goal.
The Rams looked lively early on and Jeff Hendrick went close when his shot from 20 yards was tipped onto a post by Hornets keeper Bond.
Lloyd Dyer had Watford's first clear chance when his shot from inside the box was saved by Jack Butland.
The Rams keeper denied the Hornets a number of times, in what could prove to be his last appearance with his loan deal from Stoke set to end next week.
The England international thwarted Troy Deeney and Fernando Forestieri before the Argentine-born Italian striker was denied another attempt by Craig Forsyth's tackle.
However, it was derby who took the lead when Ibe chested down Johnny Russell's pass before curling a shot past Bond.
Deeney was denied again by Butland and Forestieri fired wide twice, but Munari levelled matters soon after when he beat the goalkeeper from inside the box.
But Derby responded positively again and, after Forsyth's attempt was blocked by Bond, Bryson found the net with his side's second long-range strike of the match.
Watford poured forward in search of a second equaliser, but Butland ensured the Rams claimed all the points to move three clear of Bournemouth at the top.
Watford manager Slavisa Jokanovic: "We played the first 45 minutes without energy. We didn't play a good game and we didn't press them really. With the goal, we were a little bit scared.
"We weren't being brave and played many passes at the back slowly. We had many problems in the first 45 minutes."
Derby manager Steve McClaren: "I thought we'd lost our moment. We needed a second goal and we should have had that. We were losing it, having dominated the game for an hour.
"We played great possession football, some great chances, a great goal and were in the driving seat and in control. But you can't go through 90 minutes at a place like Watford with the quality they've got and not expect to come under some pressure."
- 39Bassong Nguena
- 12DoyleyBooked at 84mins
- 5AndrewsSubstituted forMunariat 62'minutesBooked at 90mins
- 8TozserBooked at 90mins
- 24IghaloSubstituted forVydraat 45'minutes
- 23DyerSubstituted forAnyaat 75'minutes
- 9DeeneyBooked at 90mins
- 6KeoghBooked at 13mins
- 19HughesSubstituted forBrysonat 66'minutes
- 11RussellSubstituted forCouttsat 90+1'minutes
- 44IbeSubstituted forDawkinsat 74'minutes
- Keith Stroud
- Shots on Target
Second Half ends, Watford 1, Derby County 2.
Corner, Derby County. Conceded by Daniel Tözsér.
Daniel Tözsér (Watford) is shown the yellow card for a bad foul.
Chris Martin (Derby County) wins a free kick on the left wing.
Foul by Daniel Tözsér (Watford).
Troy Deeney (Watford) is shown the yellow card.
Gianni Munari (Watford) is shown the yellow card for a bad foul.
Simon Dawkins (Derby County) wins a free kick in the defensive half.
Foul by Gianni Munari (Watford).
Substitution, Derby County. Paul Coutts replaces Johnny Russell.
Jeff Hendrick (Derby County) wins a free kick in the defensive half.
Foul by Daniel Tözsér (Watford).
Corner, Watford. Conceded by Jack Butland.
Attempt saved. Ikechi Anya (Watford) left footed shot from the left side of the box is saved in the centre of the goal. Assisted by Matej Vydra.
Corner, Watford. Conceded by Richard Keogh.
Corner, Watford. Conceded by Ryan Shotton.
Attempt blocked. Matej Vydra (Watford) right footed shot from the centre of the box is blocked. Assisted by Ikechi Anya.
Corner, Watford. Conceded by Cyrus Christie.
Lloyd Doyley (Watford) is shown the yellow card for a bad foul.