Sheffield United emerged deservedly victorious from a feisty and energetic Boxing Day battle at Bramall Lane.
The hosts responded well to a Rams equaliser early in the second-half to eventually go on and win a game that really came to life after the break, United the stronger side for much of the encounter and showing far more in the way of attacking threat throughout.
Derby were punished for not being strong enough against another of the top sides in the division, and with sterner tests to come over the next week they will need to develop much more resilience under pressure if they're to maintain their play-off place.
In a lively opening couple of minutes, David McGoldrick curled an effort inches past the post for the hosts from just outside the penalty area, then the Rams went up the other end and Mason Mount forced keeper Dean Henderson to parry a low shot away from a narrow angle.
Billy Sharp then brought the best out of Scott Carson after connecting with an Enda Stevens' knock down but seeing the Rams keeper deny him from close range.
Jayden Bogle curled high and wide moments later as again the visitors responded well, but something of a lull then descended in terms of chances as neither side was able to get a hold on the game and both were wasteful in possession.
Then, on 32 minutes, a sublime through ball from Tom Huddlestone sent Harry Wilson in on goal but after rounding Henderson, his shot from a fairly narrow angle was cleared off the line by George Baldock with what was the best chance so far.
Wilson then swung a free-kick in from out wide which Chris Basham nodded only inches wide of his own goal, but four minutes before the break, it would be the hosts who would go in front.
McGoldrick freed Jack O'Connell down the left hand side and his cross was headed down and into the corner by Sharp, out of the reach of Carson who was diving full length, and that was how it stayed until half-time.
After United had edged the early stages of the second-half, the Rams got level six minutes in. A hand ball on the right hand edge of the penalty area led to a free-kick in very much 'Harry Wilson range', and sure enough the Welshman fired his effort into the top corner of the net off the underside of the crossbar. Henderson didn't even move.
Ollie Norwood blazed high over the bar minutes later as the Blades responded, the midfielder in lots of space when the ball broke to him on the edge of the penalty area, then Wilson hit another free-kick from nearly 40 yards which narrowly missed the top corner of the goal.
Sharp headed over the top from a fine Enda Stevens cross on 63 minutes as the game continued to spark into considerable life, and the Blades would be in front just a minute later.
John Fleck's diving header forward released McGoldrick in on goal and he was able to precisely lob Carson and the ball bounced into the net to send the home crowd wild.
Derby introduced George Evans and David Nugent, the latter joining Jack Marriott up top, as they tried to find another leveller, although Sharp nearly made it 3-1 with an overhead kick which was straight into the hands of Carson.
Sharp again went close a few minutes later, this time heading inches wide from a left wing cross, but the crucial third would come with six minutes to go.
A free-kick from out on the left was headed back across goal by John Egan and recent sub Leon Clarke headed towards goal and in, although a key touch from Bogle seemed to take the ball out of Carson's reach.
The Rams had little more to offer after that as the hosts saw the game out with few alarms, a deserved three points going to Chris Wilder's men.
Sheffield United: Henderson, Baldock, Stevens, Fleck, O'Connell, Basham, Sharp (c), Egan ,Norwood, McGoldrick, Duffy (Clarke 80)
Subs not used: Clarke, Coutts, Stearman, Johnson, Moore, Cranie, Washington
Derby County: Carson, Wisdom (Waghorn 84), Bryson, Tomori, Keogh (c), Wilson, Mount, Jozefzoon (Nugent 69), Marriott, Bogle, Huddlestone (Evans 69)
Subs not used: Pearce, Roos, Holmes, Bird
Ref: Geoff Eltringham
Att: 28,974 (2,229 away)