Darren Sarll’s side started the day 15th in England’s fourth tier but they dominated the tie throughout, with Joe Martin’s corners repeatedly causing Jaap Stam’s team problems.
Danny Newton headed over from 12 yards after six minutes before defender Ben Wilmot forced goalkeeper Anssi Jaakkola into an acrobatic save on the half-hour.
The Championship side’s only effort on target in the opening half came four minutes before the break, but loanee Stevenage goalkeeper Tom King brilliantly saved Dave Edwards’ flicked header from point blank range.
Newton’s neatly struck half-volley on the turn from 25 yards flashed inches past Jaakkola’s post as Stevenage started the second half well, and Martin saw two curling free-kicks saved by the Royals goalkeeper.
Jaakkola kept his side in the game with a flying parry to keep out Jack King’s goal-bound volley from the edge of the box on the hour as Stevenage deservedly earned a replay.
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