Teddington, with Jason Laslett - Britain's Olympic captain - to the fore, opened in aggressive mood and only a series of fine saves by Richard Hargraves (deputising for Simon Mason who is recovering from a back operation) in the Reading goal kept them at bay.
With Reading failing to take advantage of the temporary suspension of James Wallis, their hold on the Cup was looking precarious. But a little magic by their young striker Mark Pearn and a gem of a pass put Mark Hoskin in to score with their first real attack in the 24th minute.
Within three minutes Teddington were on terms. Andy Billson, having fumbled a half-chance, made no mistake as Nick Conway recovered the ball and returned it to him.
Reading no doubt will feel robbed at not receiving perhaps two penalty strokes early in the second half but it was not to be, with the winner coming in the 58th minute from Conway at a well-worked penalty corner.
Reading moved Jon Wyatt forward but with Laslett in commanding form they were able to make little impression on the Teddington defence. Their fightback was also hampered when their goalscorer Hoskin was suspended for the closing minutes.
Reading: R Hargraves; C Oscroft, R Todd, J Wyatt (capt), A Holden, M Hoskin, J Slay, G Edwards, S Ashdown, M Pearn, K Sanders. Substitutes used: S Briscoe, J Loose, A Jones.
Teddington: J Ebsworth; T Moore, S Nicklin, S Dawkins, A Colclough (capt), J Wallis, J Laslett, P McGuire, N Conway, J Hauck, A Billson. Substitutes used: P Way, G Read, D Haydon.
Umpires: D Collier and A Hoyes (SCHUA).