Ed Still secured his first win as Watford manager as goals from Luca Kjerrumgaard and Mamadou Doumbia goal earned a 2-0 victory over Derby at Vicarage Road.
The triumph marked a first home game for Still, Watford's third permanent manager of the season, and moved the hosts level on points with Derby in the congested promotion play-off race.
It also extended a remarkable streak in this fixture, with Watford recording their sixth successive win over their opponents.
Rams manager John Eustace, a former Watford captain, has yet led a side to victory against the Hornets.
The visitors might have sensed the worst when Watford's first attack produced a goal after only five minutes.
Edo Kayembe met an Othmane Maamma cross, but saw his shot blocked by the diving bodies of Matt Clarke and Dion Sanderson before the ball eventually squirmed away for Kjerrumgaard to drive it into the net.
The home side's bright start continued when Jeremy Ngakia tested Derby goalkeeper Josh Vickers with a powerful low shot at his near post.
Maamma limped off midway through the half. He was replaced by Giorgi Chakvetadze, whose first act of note was to drive unchecked infield. Unfortunately for the hosts, his shot was straight at Vickers.
The game turned into a midfield arm-wrestle for the remainder of the half, except for a rapid home break in added time, which ended with Kayembe lifting his shot narrowly over the crossbar.
A hectic second half saw play swing from one end to the other. It began with efforts at both ends.
First, Joe Ward drove a shot from outside the area into the advertising hoardings. Almost immediately, Nestory Irankunda responded with an even more ferocious effort that was beaten away by Vickers.
The temperature inside Vicarage Road was turned up by the introduction of former Luton striker Carlton Morris off the Derby bench to a chorus of boos.
Suddenly, the Watford faithful had to break off their baiting of Morris when Irankunda raced back on to the pitch following an injury and bore down on the visting goal, but could not beat Vickers with his shot.
They were then howling for a penalty when Irankunda's replacement Kwadwo Baah tripped over the leg of Sanderson, only for referee David Webb to wave away the home side's appeals.
Watford clinched victory in the 90th minute when two substitutes combined, with Marc Bola accepting a smart pass inside before his low cross was flicked home by Doumbia.
Watford's Ed Still:
"It is all about the players. I'm just there like a wally on the side of the pitch jumping up and down.
"It was special to be able to give the fans something to cheer about. And to be able to start the game the way we did, to get an early goal and not to step back too much after that.
"To send everybody home happy and hopeful for the coming weeks was great. And we also saw a team that is connecting again, not just as footballers, but as people. That is massive.
"We've tried to bring as much fresh energy and as much clean energy as possible.
"We did a huge amount of defensive work this week and it's a good job we had four days on the training pitch to be able to prepare."
Derby's John Eustace:
"Watford wanted the game more than us. We lost too many duels and we were too slow on the ball. This is a game we must learn from.
"The players have said it themselves, that as a group we let ourselves down today and we need to be better.
"We didn't compete well enough every time we got into the final third. We didn't look after the ball well enough and our decision-making wasn't good enough.
"We've been on a good run, but in the Championship you always get games like this so we don't get carried away with the highs and the lows.
"This gives us a reminder that if we think we've arrived, we're in trouble."
