No wonder this was the hottest ticket in town; this was a night the red half of Bristol will simply never forget. As the final whistle blew, a sea of Bristol City supporters stormed the pitch while manager Lee Johnson was still recovering after hurtling down the touchline, catching a delirious ballboy in mid-flight before swinging him around his hips, by which time the celebrations were already well under way. Bristol City had deservedly dispatched Manchester United for the first time since 1978, with a brilliant 93rd-minute winner teeing up a date with Manchester City in the Carabao Cup semi-finals.

Korey Smith, the matchwinner who crashed home with only seconds remaining, was mobbed before leaving the pitch “like John Wayne”, according to Johnson while Joe Bryan, the Bristolian and academy graduate, who opened the scoring in equally emphatic style, was carried towards the dressing room. Johnson had urged his players to make themselves heroes but they did that and more, etching their names into history after felling the holders in the sweetest manner imaginable. In doing so, the Championship side have now beaten four Premier League opponents this season, more than both Swansea City and West Bromwich Albion. Another fearless performance like this and they might make that five.

This was always going to be a special occasion, under the lights inside at a sold-out – revamped and rocking – Ashton Gate as the Robins duelled with United for the first time since 1980. The ambition here is to make these meetings a more regular occurrence, with City third in the second tier and vying for promotion. José Mourinho stuck to his word by naming a strong team here although David de Gea and Nemanja Matic did not travel to the West Country. Luke Shaw, however, made his first start since April.

It was Smith – a £350,000 signing from Oldham Athletic – and City’s one change, the incoming former United goalkeeper Luke Steele, who made the greatest impression, with the latter twice superbly denying the substitute Romelu Lukaku. Smith’s opposite number Sergio Romero, though, was kept more busy during a frenetic first half of action, with Josh Brownhill’s dipping drive forcing him to punch clear early on while defender Hordur Magnusson also went close.

United, though largely underwhelming, twice struck the woodwork inside 21 minutes, through the returning Zlatan Ibrahimovic and then Marcus Rashford. Ibrahimovic then skewed a volley horribly wide and into the rebuilt South Stand. When Smith drove into the box he almost laid the ball on a plate for Bobby Reid only for Daley Blind to pour cold water on the move, intercepting just as the forward looked to pull the trigger.

Aden Flint, who has a knack for coming up with the goods having scored six times already from centre-back this season, did put the ball in the net when poking home after blocking Romero’s goal-kick but the referee, Mike Dean, intervened with the defender already wheeling away. It caused a kerfuffle on the touchline, too, with Mourinho’s assistant, Rui Faria, and Bristol City assistant coach Dean Holden briefly exchanging words.

After the interval, a couple of quickfire late challenges on Paul Pogba and then Anthony Martial presented the visitors with the chance to test Steele. Test him they did, with the City goalkeeper diving low to his right to clear Rashford’s effort. Then City flew forward, with Reid flashing a shot into the side-netting after eluding Victor Lindelof.

City’s next move left a significant mark, though. Reid played a fine through ball into Bryan, who raced down the left before blasting the ball across Romero and into the corner of the net. United, as poor as they had been, were shell-shocked while the home dugout exploded to life as Johnson, Holden, assistant coach Jamie McAllister, kit man Scott Murray and goalkeeping coach David Coles celebrated wildly in an impromptu mosh pit.

Ashton Gate was bouncing, but the joy was short-lived. Six minutes later, Pogba ran in to blockade of red shirts, winning a soft free-kick out of the midfielder Smith. Ibrahimovic stood over it before hammering it low around the wall and past Steele, who seemed to be caught unsighted. Ibrahimovic simply wagged his finger in celebration.

Then came Lukaku in place of Blind but it was Bryan who found the next opening, his tame right-footed effort being easily gathered by Romero after he had read Reid’s nutmeg. Mourinho then introduced Mkhitaryan – but in place of Ibrahimovic – while City went for broke, summoning the former Bristol Rovers striker Matty Taylor in place of Magnusson.

City surrendered control in search for a winner, with Lukaku’s header forcing Steele into a superb stop while Bryan did brilliantly, as the last man, to prevent Rashford from squaring for Lukaku. But then Smith latched on to Taylor’s chipped pass to provide the most incredible of finales. The rest is now history.