Substitute Al Bangura grabbed a late goal to rescue a point for Watford.
Kevin Lisbie gave Derby the lead against the run of play when he raced onto Adam Bolder's pass and trickled a low shot into the far corner.
Marlon King fired the Hornets level with a smart finish from 18 yards and later hit the post as the home side poured forward.
But Giles Barnes slid in to put the Rams ahead before Bangura made it 2-2 with a fine shot deep in injury-time.
Watford manager Adrian Boothroyd:
"If we win our next nine matches between now and the end of the season I think we'll do it.
"I believe we'll get an automatic promotion spot.
"There are a lot more twists and turns to be taken between now and the
end of the season and all I'm doing now is focusing on the next game."
Derby manager Terry Westley:
"If you had said to me before the game we would go to a team chasing automatic promotion, and get a draw we would have settled for that.
"Their equaliser was controversial as the ball hit his arm and then rebounded into his path for the shot.
"If you're at home and everyone screams 'handball', maybe you get that
Watford: Foster, Doyley, Mackay, Carlisle, Stewart, Eagles (McNamee 80), Mahon, Spring, Bouazza (Bangura 45), King, Young.
Subs Not Used: Chamberlain, Chambers, DeMerit.
Booked: Mackay, Bangura.
Goals: King 35, Bangura 90.
Derby: Camp, Edworthy, Moore, Wright, Barnes, Nyatanga, Holmes, Bolder, Idiakez, Smith, Lisbie (Peschisolido 67).
Subs Not Used: Poole, Kenna, Bisgaard, Thirlwell.
Goals: Lisbie 19, Barnes 86.
Ref: A Leake (Lancashire).