City's expectant fans had to wait 75 minutes before they could go bananas, and it was their long-time favourite Micah Richards who unlocked Reading's defence where City's front line had faltered.
For all the Blues' expensive firepower mounted against their Championship challengers, it was a towering header fromRichards at a David Silva corner that finally booked a Wembley showdown with Manchester United.
Micah's resurgence in form landed him the fans' votes as Player of the Month for February, but his third goal of the campaign earned their undying gratitude as the inflatables waved and the ritual Poznan was danced.
But City's first FA Cup semi-final since 1981, another step in the right direction for Roberto Mancini and his men, looked anything but certain for long spells as Reading threatened to hold out for the replay.
Even after they had conceded to Richards' unstoppable header, they refused to accept their fate, and Joe Hart's goal came under some pressure before the referee called time on a nerve-wracking quarter-final.
Reading flattered to deceive in the opening minutes, and when Joleon Lescott had to stretch to concede a corner from Jobi McAnuff's raking cross, it looked as if they might have decided to ditch caution.
But the two ranks of four that formed soon after and dug in for the long haul suggested otherwise, and the message was clear: find your way through, if you can, and watch us try to catch you on the break.
It is a tried and tested ploy for FA Cup underdogs and best undone by a goal, of course. But having found a way through on several occasions, City were met by a goalkeeper in Alex who knew his angles and used his agility.
Silva came up with several cute passes in a first half that seemed destined to see Reading trail, only for the keeper to prove equal to whatever was thrown at him in the final instance
Or, as when Silva and Carlos Tevez essayed a dazzling duet in the penalty area, sheer weight of numbers, particularly for the well-policed Argentine, swamped any chance of putting the ball in the Reading net.
Shaun Wright-Phillips, revelling in his start and cheered to the rafters by home fans, might have done better when Silva slipped him in, the England winger taking careful aim only to hit the side-netting.
Silva's great lob five minutes later found Yaya Toure's intelligent run but the midfielder's powerful angled drive was blocked by Alex, as was Silva's own attempt after the Spaniard delightfully tricked his way past Ian Harte.
When Yaya and Tevez combined to give Silva a chance that was swiftly smothered, it was clearly going to be one of those games, and the frustrated World Cup winner thrashed his next attempt into the crowd.
Tevez, worryingly, looked below-par, and the little striker, without a goal since the 5-0 replay win over Notts County in the fourth round, made a hash of his clearest-cut chance after 56 minutes.
But Richards, who also joined in that Notts goalfest a month earlier, was waiting to make his mark and keep City on the glory trail. The dream of an FA Cup victory, in the year of 1969 hero Neil Young's passing, lives on.