For 81 minutes in a tense, hard fought affair at the Joie Stadium, the breakthrough had eluded Ben Wilkinson’s side with the visitors also proving a threat going forward.
But with just nine minutes left and the prospect of extra time looming, winger Muir, who had been brought on after an hour, made the difference firing home from close range to deservedly see us through to the showpiece final.
Now we await to see who we will play in the final – with Leeds and Millwall contesting the other semi-final on Thursday.
What happened
City stepped out seeking to atone for the heartbreaking memory of last year’s semi-final defeat at Arsenal.
However, it promised to be another tough examination for Wilkinson’s young charges with the Robins having not conceded a goal on their route to the last four after despatching Swindon, Burnley, Charlton, Stoke.
Under clear skies at the Joie Stadium and with only a slight chill in the air, it was a fast-paced start as both sides pressed for the upper hand..
It was the visitors with the first opportunity, Joseph James sending a dipping 23rd minute corner narrowly wide of City’s left-hand post.
An obdurate Bristol City defence offered stiff early resistance. The visitors packed bodies behind the ball in numbers, demonstrating just why they had proved the toughest of nuts to crack on their journey to the last four.
City meanwhile sought to stretch play and utilise our pace on either flank through Joel Ndala and Farid Alfa-Ruprecht.
Meanwhile at the other end Elijah Morrison was the next to test the City defence, arcing a 31st minute header just wide before a low Joseph James shot warmed home keeper True Grant’s hands.
In what was a high intensity encounter with so much on the line, the visitors saw three of their players succumb to hamstring injuries before the half time break, with eight added minutes the result.
And City came close three minutes into that additional time when Ndala found space down the left flank and picked out the advancing Justin Oboavwoduo only for his goal bound header to be deflected wide.
In a frantic finale to what had been a cagey opening period, City skipper Jahmai Simpson-Pusey then had the visitors scrambling again, a dipping 25 yard effort whistling agonisingly wide.
And Oboavwoduo then came even closer to that crucial breakthrough in the last of the first half added time.
The striker latched onto an under-hit back pass and rifled in a shot that evaded City keeper Joseph Duncan but which was blocked on the line by Jed Meerholz.
The second half followed a similar pattern to the majority of the opening period, with both sides desperate not to yield the advantage.
There was a brief moment of panic on the hour when an attempted City clearance ricocheted off Robins striker Ephraim Yeboah but fortunately went over the bar.
Wilkinson opted to freshen things up bringing on Isaiah Dada-Mascoll for his first minutes of an injury-ravaged season along with Ashton Muir.
And there was almost an instant dividend on 70 minutes when Muir got behind the Robins backline and fed an inviting ball into the heart of the box only for Heskey to get under his shot.
However, within 60 seconds City were then breathing a sigh of relief after a twisting run and turn from Billy Phillips ended with his 20 yard shot missing the target by the narrowest of margins.
But it was City in the ascendant and our renewed sense of urgency was finally reward on 81 minutes when that man Muir made the crucial breakthrough.
Farid Alfa-Ruprecht was the architect, latching on a finely threaded ball from Kian Noble on the right byline..
The winger delivered an inviting cross into the heart of the box and the onrushing Muir made no mistake, buying home a close range shot to give us a precious advantage.
Okeke and Mukasa both then came close to adding to City’s advantage as we sought to kill the game.
But Wilkinson’s charges saw the game out in fine style to seal a hard fought and memorable success.
How we lined up
True Grant was in goal for City and shielded by a back four of Michael Okeke, skipper Jahmai Simpson-Pusey, Stephen Mfuni and Sebastian Naylor.
Kian Noble, Jaden Heskey and Farid Alfa-Ruprecht were in the engine room with Justin Oboavwoduo, Divine Mukasa and Joel Ndala our attacking trident.
CITY XI: Grant, Okeke, Simpson-Pusey (c)), Mfuni, Naylor (Dada-Mascoll 60), Noble, Heskey, Alfa-Ruprecht, Oboavwoduo, Mukasa, Ndala (Muir 60)
Subs: Henderson-Hall, Brits, Fapetu, Warhurst, Fletcher
BRISTOL CITY: Duncan, James, Ali (Davies 44), Campbell-Slowey, Anderson (Bak 29), Hewlett (c), Phillips, Meerholz, Nelson (Filer 12), Yeboah, Morrison,
Subs: Witchard, Kasvosve, Chaplin, Foxwell
What it means
City are through to the FA Youth Cup final where we will meet the winner of the other semi-final between Leeds United and Millwall, who meet this Thursday.
We will enjoy home advantage in the showpiece with a date and time yet to be confirmed.
What’s next
City’s Under 18s return to Under-18 Premier League North action on Saturday when we make the trip to take on Wolverhampton Wanderers.
Kick off in the Midlands is slated for 12.30pm (UK).
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