Gavin Rose brought in Kenny Beaney and Jordan Hibbert for Kevin James & Jack Dixon in the only changes from the team beaten at Needham Market.
The performance could not have been more different to Saturday's as Dulwich were strong at the back and disciplined all over the park as they nullified the free scoring Bognor side.
It was Dulwich that was on the front foot for much of the game and the first save from Smith in the Bognor goal saw him comfortably hold a deflected 12th minute effort from Ashley Carew.
Dulwich were using the wings well and controlling the tempo of the Match but had an alarm in the 16th minute when Preston Edwards & Matt Drage collided as the keeper came for a harmless looking cross but the ball was scrambled clear.
Two minutes later, good play from Bognor saw a shot on the turn go inches wide. Bognor also had a penalty appeal waved away before Dipo Akinyemi produced a scuffed effort after he cut inside.
Nyren Clunis had a good chance just before the half hour but his effort was well saved low to his left by Smith and, with half time approaching, Smith also held a header from Matt Drage.
Half Time 0-0
Jack Dixon came on for the injured Kenny Beaney at the start of the 2nd half and Dulwich opened brightly as they forced a number of corners.
However, the first clear chance did not arrive until the 58th minute. The impressive Roman Michael-Percil set up Dipo Akinyemi but his rushed effort was off target from 12 yards.
Nyren Clunis was only just wide and Mitchell Nelson had a header saved as The Hamlet looked the most likely to break the deadlock. But it was to be the home side that had the gilt edged chance to score with 16 minutes remaining, a clumsy challenge seeing the referee point to to the spot.
Jason Prior stepped up but Preston Edwards got a strong hand to his effort to push it over the bar.
Despite the efforts of the players, the match seemed to be drifting to extra time when Dulwich struck in the second minute of time added on. Dipo Akinyemi was brought down 25 yards out and Ashley Carew struck the ball over the wall, and past the unsighted and statuesque Smith, to spark delirium on and off the pitch.
Bognor mounted one final attack but the long throw was cleared to Rhys Murrell-Williamson who accelerated away and set up Akinyemi, but his effort was blocked.
This proved the last action as the referee's whistle confirmed Dulwich's place in Monday's final at East Thurrock.
Updated 19:44 - 2 May 2016 by Liam Hickey