Korey Smith sensationally stunned Manchester United by dumping the holders out of the Carabao Cup.
Midfielder Smith sparked wild scenes of celebration on the touchline from boss Lee Johnson and a full-time pitch invasion after he latched onto Matty Taylor's ball over the top and lashed it past Sergio Romero to clinch a famous triumph for the Championship side.
The best first half chances fell to United. Ibrahimovic turned a first-half volley onto the bar before Marcus Rashford cut in off the left and hit the post.
But Bristol City struck first in the 51 minute to lift the roof off Ashton Gate. Marlon Pack slid the ball through to winger Joe Bryan who gave Sergio Romero no chance with a thumping, rising drive that flew across the United keeper and into his top cormer.
But seven minutes later United were level when Zlatan Ibrahimovic netted his first goal since his return from seven months out following a horror knee injury.
Pogba, back from a three-game ban, was brought down just outside the City box and captain for the night Ibrahimovic dished out the punishment by smashing a 25 yard free-kick through a gap in the wall and past former United keeper Luke Steele.
But United failed to find a winner despite sub Romelu Lukaku testing Steele three times paving the way for Smith's last-gasp heroics.
Here are five talking points
1. Bristol City rewarded for patience
Times like these and memorable nights like this are vindication for Bristol City owner Steve Lansdown.
He easily could have sacked boss Lee Johnson last season when a promising start turned into an alarming slump featuring a club-record eight straight league defeats.
Then, it seemed the only place the Robins were flying to was League One.
But Lansdown kept the faith with Johnson when so many of his twitchy Championship counterparts pulled the trigger and now City are being rewarded.
They are right in the hunt for promotion having transformed last season's relegation battle into a push for the Premier League.
And Johnson gave them one of the most famous nights in their history by steering them to this unforgettable win.
These are wonderful times to be a Bristol City fan.
2. Robins show their quality
After his players beat three Premier League teams to reach the last eight, boss Lee Johnson described this glamour quarter-final tie as “another chance for them to enhance their reputations on a national scale.”
They didn't disappoint as Bristol City gave Jose Mourinho's side a proper run for their money.
Their defence rarely gave United a clear sight of goal until the visitors turned up the heat after going behind and then, aside from Zlatan Ibrahimovic's equaliser, found their former keeper Luke Steele in inspired form.
Their midfield pressed relentlessly and hassled and harried United to distraction.
They carried an attacking threat too in the shape of left-winger and match-winner Joe Bryan, Jamie Paterson and Bobby Reid.
Given so many Premier League sides park the bus against the big boys Bristol City's approach was refreshing to see.
And it was easy to see why they are in the hunt for promotion to the Premier League.
3. Ibrahimovic produces when needed
In seven months out due to his horror knee injury, Zlatan Ibrahimovic has understandably lost a little sharpness.
That much was evident at Ashton Gate in his first start since his return, not least when he sliced a shot out for a throw-in about ten minutes into the second half.
But he hasn't lost his talismanic qualities.
That was also evident at Ashton Gate when United's captain for the night smashed in United's free-kick equaliser.
United were on the ropes after falling behind in the 51 minute and Bristol City's tails were up.
But Ibrahimovic produced when United needed something, just as he did so often last season.
4. Pogba makes his return
Jose Mourinho will hope Paul Pogba got the rustiness out of his game against Bristol City.
Pogba looked like a player trying to rediscover his rhythm after serving a three-game ban.
Little went right for him in a frustrating first half in which he was fortunate to escape punishment for a challenge on Marlon Pack.
It begun with him robbed of possession after dilly-dallying not far outside his box and giving away a foul and ended with yet another attempted pass being intercepted.
There were some nice flashes and clever touches and interchanging with Anthony Martial as he moved to the left wing to allow his fellow Frenchman to move inside.
But his below par night was summed up when he burst through on goal in the closing stages only for his touch to let him down at the crucial moment.
5. Lindelof getting better
After his shaky start to life at Manchester United, there were more promising signs from Victor Lindelof at Ashton Gate.
Championship opposition Bristol City may have been but this was an awkward tie, against a lively attack in a raucous atmosphere.
It appeared to ruffle the feathers of a few of Lindelof's teammates but, in contrast, his calm and composure stood out.
It was all a far cry from his first few months at Old Trafford where nearly all of his early displays featured so many costly mistakes.