The semi-final had to be switched from Aldermaston’s Hampshire Premier League ground to the home of Southern League Fleet.
The visitors started kicking up the slope and had the first chance in the opening minutes, when Michael Porter drove down the left and squared the ball, but Carmel Tonna fired just wide.
Soon after, Aldermaston were awarded a penalty for handball, but Ryan Pryce saved from Kai Parton-Edey.
Then, on 15 minutes, Matt Wilkins hit the post for the HPL outfit and it looked like it was not going to be their night.
However, Aldermaston took the lead on 25 minutes, as Liam Tackley passed for Wilkins to score.
Fleet, who had been limited to long range efforts, equalised from the penalty spot after Craig Davis was brought down in the area by Alex Sylvester.
The striker dusted himself down and scored from the spot to make it 1-1 at half-time.
After the break, both sides went for the win, but the game looked to be heading for extra-time until Aldermaston scored the winner with a minute to go.
Tackley released Wilkins and he slotted home to give Aldermaston a deserved victory.
They will now face Tadley Calleva in the final on Wednesday night (kick-off 7.45pm) at Barlow’s Park.