The first half was a fairly quiet affair, with Slough having more of the play but Aylesbury creating the better chances, most notably in the first few minutes when Steve Clark and Dwain Clarke both went close.
Shortly before the break, both sides were reduced to ten men, after Slough's Junior Haynes tangled with Frank McCormack. Haynes received a straight red card as a result, and McCormack a second yellow.
The reduction in personnel led to a more open second half, in which the home side looked to be getting the upper hand. Adam Wheeler tipped over Bartley's overhead effort, whilst Ullathorne went close with a near post header, and Bartley was denied a run on goal by a late offside flag.
But United delivered the sucker punch following a Dwain Clarke free kick. It was from almost exactly the same spot where he had scored in the league game the previous month ? this time he hit the post, but Ollie Stanbridge was on hand to bundle home the rebound and maintain his impressive scoring record against the Rebels.
The second goal was also created by Dwain Clarke, who chased a lost cause down the left flank, did superbly to win the ball and deliver a cross, which Stanbridge headed home.
Injuries in the last few minutes saw United holding on with nine and, briefly, eight men ? but the result was never in doubt.