Hornchurch booked a trip to Wembley for the FA Trophy final after shocking Notts County in a penalty shoot-out at Meadow Lane.
Isthmian League Urchins had already produced a string of upsets on their way to the last four, knocking out Tonbridge Angels, Dulwich Hamlet, King's Lynn Town, Maidstone United and Darlington from above them in the pyramid.
And they did it again, snatching a dramatic injury-time equaliser through Liam Nash to force penalties, with Joe Wright saving from Jake Reeves before Chris Dickson slotted home in style.
New Magpies head coach Ian Burchnall named a strong side, having replaced Neal Ardley in the hotseat during the week following a 2-2 draw at Yeovil.
And Jordan Barnett flashed in a cross from the left inside the first minute, looking for Kyle Wootton, before Urchins were able to clear the danger.
Sam Higgins then turned neatly on the left touchline and advanced towards the edge of the County box, before seeing his shot deflected narrowly wide for a corner, which the hosts cleared up to halfway.
County, beaten in the semi-finals by Harrogate Town last season, enjoyed the majority of possession in the opening stages, but Urchins kept their shape well only to fall behind on nine minutes when Wootton got up to head home from Barnett’s left-wing cross.
And only a superb save from Wright, diving low to his right, denied Wootton a second less than two minutes later as he got up to meet an inswinging corner from Michael Doyle to nod downwards towards the foot of the post.
A foul on Remi Sutton gave Hornchurch a free-kick chance, some 30 yards out, in a central position on 18 minutes but Lewwis Spence saw his delivery into the box comfortably claimed by Sam Slocombe.
And there was another scare for the visitors two minutes later as Enzio Boldewijn made space on the left and crossed for Wootton, who headed over from close range.
Joe Christou was shown a yellow card following a heavy challenge on Calvin Miller moments later, which had County players incensed, but Urchins were then frustrated when Mickey Parcell was left in a heap and no further action was taken.
Connell Rawlinson was booked for the home side on 29 minutes, following a challenge on Higgins, but Nash saw his free-kick headed clear and a second cross run through to Slocombe.
Wootton headed over again, when Boldewijn flicked on Barnett’s left-wing cross on 36 minutes, and then saw a far-post header from a deep cross grabbed by Wright.
And Urchins were back on level terms seconds later when Spence received the ball from Sutton and let fly with a left-footed shot from around 25 yards, which deflected off the shins of Rawlinson and beat the wrong-footed Slocombe to find the bottom corner of the net.
County were back in front on 41 minutes, though, when Miller found Dion Kelly-Evans on the right and his deep cross picked out Boldewijn to bring the ball down, as Parcell claimed he had been fouled, and tee up Ruben Rodrigues to slot home.
But the visitors squared matters for a second time during stoppage time as Spence won the ball in midfield and played it through to Jordan Clark on the left, to slide a cross perfectly into the path of Nash to steer home.
The second half was barely 30 seconds old when Higgins headed the ball on and Ellis Brown sent a left-footed shot on the turn whistling over the crossbar from the edge of the box.
And that appeared to rattle County, who could not settle as quickly as they had at the start of the match, with Urchins hunting them down across the pitch.
The home side were awarded a free-kick 25 yards from goal, just left of centre, on 52 minutes after a foul on Doyle, but Reeves fired over the wall and high over Wright’s crossbar.
Both sides made their first change before play could restart, with Urchins boss Mark Stimson - a four-time winner of the Trophy - sending Charlie Ruff on for Christou, and Wright held onto a fierce drive from Barnett at his near post, after he had been played in by Boldwijn on the left.
Then Brown seized on the ball in midfield and found Ruff in space on the left, with his dangerous cross into the six-yard box contested by Higgins and Slocombe, who were both left down on the turf in need of treatment.
Both recovered to continue, with Slocombe punching a Sutton cross clear as Urchins pieced together a good move on the left just past the hour mark, and County had penalty claims turned down when Wootton went down in the box on 65 minutes.
Higgins made way for Ghana international Dickson midway through the second half, as County also made a second change for the final quarter of the match, which was now hanging on a knife edge.
And great work by Parcell denied Wootton after Jimmy Knowles had set up the chance for the striker, who checked back onto his left foot at close range but saw his effort blocked by the Urchins defender.
County then started to see more of the ball, with Urchins skipper Spence picking up a booking for a trip on Reeves, and the home side took the lead for a third time from the resulting free-kick as Doyle delivered to the back post and Mark Ellis headed the ball back, before it was turned home from inside the six-yard box by substitute Eli Sam with 12 minutes left, having only just joined the action moments earlier.
Knowles fired a rising drive over the Hornchurch crossbar as the clock ticked down inside the final five minutes, with an additional five minutes then allowed for stoppages.
And Urchins levelled for a third time just 30 seconds into that period, when Dickson controlled the ball on the edge of the box and picked out Ruff on the left side of the box, with his header being turned home by Nash.
Doyle hobbled off to leave County to finish the tie with only 10 men, before the final whistle went and it went to penalties.
Wootton converted the first spot-kick, before Clark slotted home for Hornchurch, despite a shout from the sidelines which led to some words being exchanged between the two dugouts.
O'Brien fired into the top corner with County's second effort, with Nash seeing his reply find the corner of the net after hitting the trailing leg of Slocombe to make it 2-2.
Reeves was then denied by Wright, who dived to his left and parried, before Muldoon put Urchins 3-2 up.
And after Knowles levelled for the hosts, Rickie Hayles put Hornchurch 4-3 up, before Sam squared matters again.
That left Dickson with the chance to send Urchins to Wembley, which he took in style as he fired into the left corner of the net before celebrating with Wright as teammates flooded in to join them.
Now it's off to Wembley on May 22 to face Hereford, who beat Woking 1-0 in the other semi-final.
Notts County: Slocombe, Barnett, Ellis, Rawlinson, Kelly-Evans, Miller (Sam 74), Doyle, Reeves, Boldewijn (Knowles 67), Rodrigues (O’Brien 53), Wootton.
Unused subs: Pilling, Turner, Chicksen, Golden.
Hornchurch: Wright, Parcell, Sutton, Clark, Hayles, Muldoon, Brown (Stimson 89), Spence, Higgins (Dickson 67), Nash, Christou (Ruff 53).
Unused subs: Thackway, Winn, Hassan, Cooper.
Referee: Peter Wright.
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