New boy Michael Proctor grabbed a debut double as Ronnie Moore's Rotherham romped to a stunning victory.
Proctor arrived in a swap deal 24 hours before from Sunderland, with Millmoor striker Darren Byfield heading for the Stadium of Light, and stole the show with a first-half penalty and a 78th minute header.
Promotion hopefuls Reading were close to an opener after six minutes but a timely challenge from Shaun Barker halted ex-Miller Shaun Goater.
And when Lloyd Owusu, on loan from Sheffield Wednesday, fired in a 13th minute cross John Salako's header was turned away by Mike Pollitt.
The Royals went in front after 19 minutes thanks to Goater.
The 33-year-old Bermudan international smashed in his ninth goal of the season from the penalty spot in front of the fans who adored him for seven seasons at Millmoor.
He was gifted the chance after Shaun Barker cut down Owusu as he ran onto Salako's astute through ball.
But four minutes later Rotherham were level when Proctor scored from the spot after strike partner Martin Butler was bundled over in the area by Adrian Williams.
In the 36th minute Andy Monkhouse struck with his gem. Shaun Barker's long throughball was headed out by Williams, but Monkhouse was hovering 22 yards out and slammed a stunning volley past Marcus Hahnemann.
Ex-Reading frontman Butler stretched the home side's lead when he turned in a cross from Chris Sedgwick for his tenth of the season.
The visitors were denied a second goal when Salako's rising effort was tipped over by Pollitt, but after that it was all Rotherham.
Proctor added the fourth 12 minutes from the end, heading in Darren Garner's free-kick, and might have had a hat-trick but for Hahnemann's late save.
Substitute Richie Barker added the fifth in the dying seconds, rounding the keeping and angling in a low shot.