It's advantage Leeds United after the first leg of this Sky Bet Championship semi-final after they came away from Pride Park with a narrow victory on Saturday evening.
Kemar Roofe's goal early in the second-half proved the difference as the visitors edged an encounter that was feisty at times but which the Rams failed to get a true hold on in front of a full house.
Leeds keeper Kiko Casilla didn't have a save to make throughout, any efforts Derby had flying high, wide or into United defenders in a game where both sides proved hard to break down.
That exception came when Roofe finished well for the winner, Rams keeper Kelle Roos having to pull out a couple of good stops to deny the visitors any further goals.
It all means a tough job lies ahead for Derby as they travel north on Wednesday night, but in a week where remarkable comebacks have become the norm, they will take solace that United's advantage is only a single goal.
If they fail to overturn it in Yorkshire, however, this game will be looked at as their golden chance to have got a true grip on the tie.
The first effort of note came six minutes in when Tom Lawrence curled wide from just outside the penalty area, then Harry Wilson fed David Nugent with a neat through ball but the striker's shot was deflected over the bar.
Mateusz Klich was well wide with a drive from distance on 11 minutes as the visitors got into the attacking third for the first time of note, then Stuart Dallas was much closer with a curled strike from 25 yards which dropped just over Roos's crossbar.
Leeds then lost defender Adam Forshaw to injury midway through the first-half, Jamie Shackleton replacing him, the visitors having edged ahead in terms of controlling the game as Derby dropped deeper and their strong start faded, along with chances for either side.
Indeed, half-time arrived with no goals to show for a largely disappointing first period.
Jack Harrison had an early second-half chance blocked by Richard Keogh as Leeds again started on the front foot, and they got their goal on 54 minutes.
Lawrence won the ball with a sliding tackle just inside his own half that only had the effect of freeing Harrison out on the left and his superb low cross to the back post found Roofe who finished well first time.
Two minutes later, Roofe nearly scored again but this time saw Roos push his effort away for a corner as Derby were exposed at the back.
Derby responded by introducing Jack Marriott for Nugent, the latter having struggled all afternoon with a general lack of service but also in possession.
The result was some better attacking pressure from the Rams, Scott Malone's low ball into the six-yard box being inches from any interested parties and a couple of free-kicks in dangerous areas not being capitalised on.
The Rams thought they had a penalty on 77 minutes when Dallas appeared to foul Jayden Bogle as he tried to reach Wilson's pass, ref Craig Pawson awarding the spot kick but reversing his decision after consulting his assistant who decided that the Rams defender had instead been the man to commit the foul as the players came together.
That riled the home support but Leeds kept their composure and sub Shackleton's volley was parried by Roos as United looked to put daylight between themselves and the hosts, the introduction by Frank Lampard of Tom Huddlestone for Lawrence soon afterwards suggesting the priority was on preventing the lead being doubled rather than wiped out.
That plan worked, the game fizzling out as Leeds ultimately held on to take a valuable lead back to Elland Road in four days' time.
Derby: Roos, Tomori, Keogh (c), Wilson, Mount, Lawrence (Huddlestone 86), Johnson, Holmes (Bennett 70), Nugent (Marriott 64), Bogle, Malone
Subs not used: Carson, Jozefzoon, Evans, MacDonald
Leeds: Casilla, Ayling, Forshaw (Shackleton 23), Cooper (c), Roofe (Clarke 80), Dallas, Hernandez, Harrison, Phillips, Berardi, Klich.
Subs not used: Peacock-Farrell, Brown, Struijk, Gotts, Bogusz
Ref: Craig Pawson
Star Ram: Duane Holmes