The Millers, hit with the penalty by the Football League last week for fielding an ineligible player, won it through goals from Matt Derbyshire and Lee Frecklington in the space of six second-half minutes and it continues a remarkable period of success for the club.
While all the talk this week has been of Bournemouth's rise to prominence from adversity, the South Yorkshire club have been on a similar journey, having also started the 2008/09 season in League Two with minus 17 points and under boss Steve Evans they have won back-to-back promotions and now booked their place in the second tier for another year.
They were made to do it the hard way with the points deduction, but this victory means they can go to Leeds on the final day of the season with no pressure on, despite a nervy ending after Oliver Norwood's late strike for Steve Clarke's side.
All the focus in the build-up to the game was the prize on offer to the Millers but Reading, woefully out of form and now without a win in nine, had clearly not read the script.
After an initial opening burst from the fired-up hosts, where Danny Ward drilled a cross-shot just wide, the visitors looked as if they were the ones with everything to play for.
They were going into every challenge full-blooded and Chris Gunter showed no mercy as he piled through Danny Lafferty, sent the Northern Ireland international flying over the advertising hoardings, wiped the linesman out and also saw a ball boy require lengthy treatment that ended in the youngster being carried away on the stretcher.
But for all their bluster, Reading did not threaten the Millers goal and it was the hosts that ended the first half strongly.
Top scorer Derbyshire drilled over and then hooked wide, with the best chance falling to Frecklington in between those two efforts.
The midfielder's volley from the edge of the area was too hot for Mikkel Andersen to handle, with the shot slipping through the keeper's grasp but landing just wide.
And a rampant two-goal salvo in six minutes at the start of the second period answered their fans' prayers.
In the 52nd minute Ward made headway down the left and sent in a dangerous cross which Derbyshire prodded home at the near post with Andersen stranded.
Then it was almost a carbon copy soon after, but this time Frecklington tapped in at the far post after another Ward centre as the Millers clinched survival.
Reading's soft underbelly had been shown and Kirk Broadfoot almost headed a third from a Ben Pringle free-kick.
The hosts did have some defending to do as keeper Emi Martinez produced a fine save to deny Norwood's shot from distance, but there was nothing he could do about another effort four minutes from time as the Reading midfielder sent his shot flying in.
But there was to be no spoiling the Millers' party, despite a frantic finish and the final whistle saw scenes of joy at the New York Stadium.