Reading ran riot with five second half goals to clinch the Championship title.
Reading celebrate another goal as they clinch the title
James Harper put them ahead after 58 minutes, evading several tackles to score and Kevin Doyle nodded in Bobby Convey's corner six minutes later.
Substitute Jon Oster added a third after 69 minutes and Shane Long quickly headed home captain Graeme Murty's cross as Derby crumbled.
Long crowned a brilliant move with the fifth to spark off scenes of wild celebrations at the Madejski Stadium.
Reading's supporters chanted "That's Why We're Champions" as Steve Coppell's Premiership-bound side turned on the style to destroy Derby.
Chairman John Madejski applauded all sides of the stadium before kick-off as Reading celebrated top-flight football for the first time in their 135-year history.
But there was little sign of the carnage to come in a tight first-half when Derby gave as good as they got.
Derby did not enter the party spirit and a swift break saw Giles Barnes carry the ball 50 yards before firing a low strike too close to Reading keeper Marcus Hahnemann.
And Paul Peschisolido was denied the opening goal by the linesman's flag.
Every Royals attack was greeted by shouts of "ole" and "shoot" but the hosts resisted the temptation until top scorer Dave Kitson's speculative turn and half-volley sailed over.
Another Derby break ended with Hahnemann grasping Michael McIndoe's drive, the policy appearing to be shoot on sight, with Barnes scuffing his second long-range effort wide.
Convey was too slow reacting to Kitson's through ball but almost made up for it with a stinging volley which unfortunately deflected behind off the striker.
A clear-cut opportunity was finally created when Steve Sidwell exchanged passes with Kitson but blazed over with the goal at his mercy, before Derby survived a penalty shout when the ball appeared to strike Adam Bolder on the arm.
But there was no respite for Derby after the break as Reading stepped up the tempo to win the title with a flourish.
Reading manager Steve Coppell:
"I think it was fitting we went up as champions.
"We have led the pack for an awfully long time and the second half performance reflected what we've been about all season.
"The final result was the right way to do it and confirm us as champions."
Derby manager Terry Westley:
"All congratulations and the plaudits should go to Reading.
"They are an outstanding team who have secured promotion, and the championship as well, and have done it so soon.
"Reading is a well-organised club with an outstanding manager and the players have shown they want to go places."
Reading: Hahnemann, Murty, Sonko, Ingimarsson, Shorey, Sidwell, Little (Oster 69), Harper, Convey (Hunt 68), Kitson, Doyle (Long 72).
Subs Not Used: Stack, Gunnarsson.
Goals: Harper 59, Doyle 65, Oster 70, Long 74, 83.
Derby: Camp, Jackson, Nyatanga, Moore, Wright, Bolder (Bisgaard 72), Idiakez, Barnes, McIndoe, Smith, Peschisolido (Ainsworth 72).
Subs Not Used: Poole, Thirlwell, Hanson.
Ref: A Bates (Staffordshire).