Reading and West Brom face an FA Cup replay after two late penalties saw honours shared at The Hawthorns.
The Baggies seemed certain to go through when Zoltan Gera struck from the spot in the 82nd minute after Chris Makin pushed Geoff Horsfield.
But Kevin Doyle coolly netted two minutes later after Martin Albrechtsen needlessly handled in the area.
Reading had the best chances, Chris Kirkland saving well from Dave Kitson and James Harper in the first half.
Reading's intentions were clear before kick off as they made six changes to the starting XI, whereas West Brom put out their strongest side.
But the visitors nearly took the lead early on when Kitson raced through and saw his fine low drive brilliantly saved by the legs of Kirkland.
It was hard to tell that West Brom were the side in the higher league as the Royals confidently stroked the ball around and made the Baggies chase shadows.
Harper forced another save from Kirkland before West Brom had their best chance of the half, Curtis Davies prodding at Graham Stack after a lung-bursting run from the centre-half.
The second half was more frenetic but both sides saved their best until the end in a dramatic conclusion that barely fitted in with the rest of the game.
There seemed little danger as Gera's cross flashed across goal, but referee Matt Messias pointed to the spot after ruling Makin had nudged Horsfield.
Gera broke the deadlock with a well-taken penalty but Reading were quickly back on level terms after Albrechtsen had stopped the ball with his right arm.
Doyle made no mistake from the spot as the Royals earned a well-deserved replay.
West Brom: Kirkland, Albrechtsen, Curtis Davies, Moore, Robinson, Greening (Gera 72), Wallwork, Inamoto (Horsfield 53), Carter, Ellington (Campbell 53), Kanu.
Subs Not Used: Chaplow, Kuszczak.
Goals: Gera 82 pen.
Reading: Stack, Makin, Gunnarsson, Ingimarsson, Shorey, Oster, Sidwell, Harper, Hunt (Little 86), Kitson (Doyle 69), Long (Lita 59).
Subs Not Used: Hahnemann, Sonko.
Booked: Makin, Kitson.
Goals: Doyle 84 pen.
Ref: M Messias (S Yorkshire).