Albion’s PL2 side were beaten at the Madejski Stadium after two quick-fire Reading goals in the second-half.
Jamie Soule had scored his fourth goal in three games to put the young Baggies ahead, but Thierry Nevers and Adam Liddle both netted within three minutes of each other after the hour mark to secure the win for the Royals.
Michael Appleton made three changes to the team which beat Sunderland 6-0 last time out, with Brad House, Tom Solanke and Rekeem Harper coming in for Josh Griffiths, Max Melbourne and Chris Willock.
The Baggies gained an early advantage when Ethan Coleman misplaced a pass back to Myles Roberts in the Reading goal, which Soule intercepted before rounding the Royals ‘keeper and placing the ball in the empty net.
Albion nearly extended their lead despite Reading pushing forward. Rayhaan Tulloch went on a long mazy run from the edge of his own box to tee up Finn Azaz in the hosts' box, but he could only fire his strike at Roberts, who closed down his angle well.
The Royals equalised just after the hour mark as Nevers cut inside and fired a powerful low left-footed shot into the corner of the net.
Just moments later, Reading scored a second goal. A Royals trialist lofted a ball into the Albion box and when it dropped to Liddle he made no mistake, volleying home from close range.
Azaz, George Harmon and Nick Clayton-Phillips all had chances to restore parity for Appleton’s side, but the hosts managed to hold on to their lead.
ALBION: House; Meredith (White 74), Solanke, Fitzwater, Harmon; Harper, Wilding; Tulloch (Asomugha 59), Azaz, Clayton-Phillips; Soule (Ashton 81).
Substitutes: Cann, Taylor.