Chris Wood's first-half header proved the only goal of the match at Elland Road, with the result seeing Garry Monk's side jump into third place and leave Derby just outside the playoff positions in seventh.
Leeds were after Derby from the very first whistle and should have taken the lead inside the opening 15 minutes after being presented with a number of clear-cut opportunities.
Kyle Bartley then had an incredible chance to send Leeds ahead in the 24th minute, but the centre-back somehow turned the ball wide at the far post after Derby failed to deal with another deep corner.
Derby improved in the period approaching the end of the first half, but Leeds finally made the breakthrough on the stroke of the interval when Wood rose highest to head a Pablo Hernandez free kick into the back of the net.
Sloppy defending from the visitors presented Leeds with the chance to double their lead 15 minutes from time, but Ronaldo Vieira's effort was kept out by smart work from Scott Carson, before Kemar Roofe missed the target moments later.
David Nugent came off the bench for his Derby debut in the 68th minute and had a half-chance late on when he rose with Green, but the former England international made the claim as the home side closed on all three points.