Richard Cresswell's fortunate late goal saw Preston take control of their play-off tie with Derby.
A defensive header struck Cresswell eight yards from goal and dribbled past goalkeeper Lee Camp.
David Nugent scored Preston's opener after collecting Chris Sedgwick's flick and slipping the ball past Camp.
Nugent also volleyed wide and Cresswell missed the target while Derby came closest through a Mo Konjic header that drifted inches wide.
Preston dominated the opening half while the visitors, after switching to 4-4-2, greatly improved in the second half.
But having enjoyed at least an equal share of the final 45 minutes Cresswell's late goal means George Burley's team have it all to do in Thursday's second leg at Pride Park.
Derby, already without influential duo Inigo Idiakez and Grzegorz Rasiak, suffered a further blow when Michael Johnson was stretchered off after just six minutes with a knee injury.
Preston welcomed back Eddie Lewis just three weeks after an operation on his appendix and the American was soon imposing himself upon the game as the home team dominated.
His cross after eight minutes was headed goalwards by Cresswell and a mazy run from Lewis shortly afterwards opened up the Rams defence only for a poor final ball to elude Nugent.
A neat reverse pass then played Cresswell through but the striker shot wide with only the goalkeeper to beat.
Camp was quickly off his line to smother at the feet of Sedgwick as Preston continued to push forward in front of their own fans.
And the goal finally came when Nugent burst through to collect Sedgwick's pass before diverting the ball superbly past Camp with the outside of his right boot.
The half-time whistle went without Derby having mustered a shot at goal and George Burley brought on Adam Bolder for Tommy Smith at the break with Marco Reich moving alongside Paul Peschisolido up front.
Preston continued to threaten, Lewis delivering a teasing free-kick that eluded everyone.
But Konjic came close to an equaliser, heading narrowly wide from a free-kick.
And Derby noticably improved after the break, winning more balls in midfield and enjoying more possession.
The visitors thought they should have been awarded a penalty when Ian Taylor, making only his second start in three months, went down under a challenge from Brian O'Neil.
Nugent might have doubled Preston's lead with an eight-yard volley but, with Richard Jackson closing him down, the 20-year-old striker shot wide.
And in the last 10 minutes a sharp one-two presented Nugent with another difficult chance on the volley, but again he missed the target from an acute angle.
But Derby's improved second-half came to nothing when Cresswell's lucky goal extended the home team's lead.
Preston boss Billy Davies said:
"I'm pleased but it's only half-time.
"The first thing I said to the players at the end of the game was exactly that. In the first 25 minutes I thought we played some wonderful football.
"We expected them to come back into the game but it's a great result and a great performance."
Derby boss George Burley said:
"We've got a mountain to climb. Preston were celebrating as if they were already at Cardiff but let's remember what the last score was at Pride Park.
"Preston's home record is exceptional but their away record is not so good in the last season.
"We know Preston are odds-on favourites so we've got to give it our best."
Preston: Nash, Mawene, Davis, Lucketti, Hill, Sedgwick, McKenna, O'Neil (Etuhu 80), Lewis (Broomes 89), Cresswell, Nugent (Agyemang 86).
Subs Not Used: Ward, Mears.
Booked: Davis, McKenna.
Goals: Nugent 38, Cresswell 90.
Derby: Camp, Kenna, Konjic, Johnson (Mills 6), Jackson, Reich, Bisgaard, Taylor, Huddlestone, Smith (Bolder 45), Peschisolido.
Subs Not Used: Miller, Junior, Tudgay.
Ref: A Marriner (W Midlands).