Second-half goals from Andrew Wood and Nathan Clarke saw Bury St Edmunds side Gym United overcome Liverpool outfit Mayfair FC 2-1 at Solihull Moor's ATG Stadium this afternoon.
Matt Morton's side had ridden their luck in the first 45 minutes, despite Tanner Call hitting the post early on, and fell behind soon after the re-start to Tom Mooney's fierce close-range free-kick.
But that goal seemed to spur Gym into life and, with the wind at their backs, they got back on terms in the 49th minute with a belting effort from Andrew Wood before Nathan Clarke made their pressure thereafter count with what proved to be the winner with his 72nd minute header.
It means the west Suffolk side, who play in the Premier Logos Bury & District Sunday League's top flight, will be the first side from the county to contest the final of the prestigious competition which has been running since the 1960s.
Gym must wait to find out their opponents though as the other semi-final, also scheduled for today, between last season's finalists, New Salamis and Hardwick FC, was postponed to March 25 due to a waterlogged pitch.
The final is due to be played at either a Premier League or Football League stadium thought to be of roughly equal distance between the sides.
Gym's Duncan McNally was much the busier goalkeeper in the first half, pulling off three eye-catching saves, though the Suffolk side came within a lick of paint of taking an early lead with the game's first shot.
Debenham LC's Tanner Call picked up a long goal-kick in-between the lines and drove to the edge of the penalty area before unleashing a right-foot shot that came back off the right-hand post.
It was mostly Huyton-based side, also on their record run in the competition, who were asking the questions and McNally had to dive to his right to push away Mooney's free-kick in the 22nd minute before parrying away from Jamie Henders after a mistake from Nathan Clarke soon after.
Just after the half-an-hour mark the Walsham-le-Willows custodian clawed out a curling effort from Conor Roberts that was heading for the top corner, while Jack Brame saw a header deflected wide of the post in a rare chance at the other end.
Mayfair's Alex Woodcock drilled a low effort wide of the far post from a good position before McNally tipped over a corner caught by the wind, with the Liverpool side having had eight to Gym's two in the first period.
The deadlock was broken less than four minutes after the re-start when McNally was penalised for picking up what was judged to be a pass-back from the wing from player-boss Morton and Mooney rifled an unstoppable free-kick from seven yards into the roof of the net.
Gym mounted a quick response though and were level just four minutes later when they worked the ball from right to left for striker Wood who unleashed a thunderbolt with his left from 20 yards that flew into the top left-hand corner.
The Thetford Town striker had not had a sight of goal up until that point but made it his third goal of the weekend, having scored both of the Brecklanders' goals in their 2-2 draw at Newmarket Town on Saturday.
The Suffolk side immediately gained confidence and Jack Brame saw an angled drive beaten away by Josh Molloy for a corner while Wood's header from Bailey's delivery was pushed away for another before a foul was committed to end the danger.
Gym continued to build their momentum, with Clarke sending a header over from a corner before they took the lead in the 72nd minute when the same player broke away from his marker from a Bailey right-wing corner and thundered his central header beyond Molloy.
Mayfair came mightly close to levelling things up straight after though with substitute Luke Stephens slipped in down the inside right channel only to lift his shot into the side-netting.
In the 82nd minute McNally saved his side after the referee allowed a quick free-kick to be taken on the edge of the box which Woodcock fired at goal only for the Gym 'keeper to rush off his line to block.
Gym handled late pressure well thereafter and managed to break away at the other end several times with Max Melanson skying a shot after neat build-up, while Brame put an effort wide from the right.
Four minutes of added time passed with Gym United's players and staff running together at the final whistle to begin the celebrations before being loudly cheered off the pitch by the coach-load of travelling supporters.
GYM UNITED: McNally, Bond, Morton, Clarke (c), Jackson, Bailey, Bolton (White 85'), Brame, Melanson, Call, Wood (Proctor 85'). Unused subs: Viner (gk), McIntosh, Robinson.
* For more reaction, don't miss Friday's Bury Free Press