The Ryman South side host Ryman North outfit Thamesmead in their semi-final while the other tie is an all-Premier clash between Concord and Hastings.
K’s looked likely to make their Premier status count when Jack Barton gave them the lead with a long-range drive after only four minutes.
Danny Carr replied in the 33rd minute and worse was to follow for K’s before half-time when keeper Lewis Bragg was sent off.
The experienced Rob Tolfrey came off the bench to take over between the posts but he could not prevent Carr giving Dulwich the lead shortly after the interval with his sixth goal in the competition.
Erhan Oztumer made sure of a semi-final place with goals in the 53rd and 71st minutes. Dulwich then had Ryan James sent off to even the numbers, but it was too late for Kingstonian.
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