It took the full 90 minutes, one tactical rejig, five substitutes and the introduction of two recent players’ player of the year winners, but Manchester City eventually reeled in Leyton Orient.

Kevin De Bruyne’s 79th-minute winner completed a 2-1 victory in this fourth-round FA Cup tie after Orient had led at half-time through a goalkeeping own goal made by a sublime intervention from Jamie Donley.

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No shock then. No need for Pep Guardiola to worry about being sacked in the morning, as the home fans seemed convinced would indeed be the case. But Orient were exceptionally good here against the champions of England, and not in a spirit-and-sweat kind of way, but organised, clever on the ball and equal partners in an excellent Cup tie.

Afterwards Guardiola seemed to relish both the win and the occasion. “We didn’t grow up playing at Wembley, we are born in these places, in these locker rooms,” City’s manager said. “I know it’s not the perfect conditions, but this is the FA Cup, any team has the right to fight against top teams.”

Brisbane Road had been a boisterous, excitingly misty place at kick-off, packed to its 9,000 capacity. The last time these two teams played was two months before England won the World Cup. Orient’s all-time record buy is £200,000. But City still came here needing a win, and it filtered through into a fine lunchtime game.

Guardiola made nine changes from the team that lay down and waggled its legs in the air against Arsenal. Vitor Reis made his debut but was hooked at half-time. Nico González made his City debut in the key role of Rodri vacuum-filler but lasted only a quarter of the game before going off injured.

Orient were unafraid from the first whistle, playing on the break and pushing hard down the left flank. After which the game settled into a pattern of calm, surgical City possession. Ilkay Gündogan air-kicked in front of goal, a startled prod after the ball trickled right across the box to get to him.

But Orient were also sharp and focused in their attacks. Their first chance came on 14 minutes, the excellent Charlie Kelman haring away from City’s high line, but unable to find the right angle, his shot blocked by Stefan Ortega.

Then with 16 minutes gone something wild happened. The ball was punted upfield from the left-back channel. González took possession in central midfield, but was robbed by Ethan Galbraith. The ball ran loose. At which point Donley produced a moment for the ages, or certainly for as long as feels like talking about it.

His first-time shot was floated perfectly, travelling in a flat arc from a few yards beyond the centre circle, over the flailing hand of Ortega and on to the underside of the bar. From there it bounced back out, hit City’s goalkeeper, and bounced back in. Brisbane Road went nuts, bodies tumbling in the stands. As Guardiola said: “When you see this you just have to congratulate the guy.”

It was a big moment for González too on his debut, who injured his back in the leadup and was subbed off, replaced by Bernardo Silva. He could be back for Real Madrid in midweek according to his manager. For now, welcome to the pyramid. How was it for you?

City pressed hard in waves, although often there was a sense of a team undecided which route to take while walking the ball into the net. Donley cleared a Silva shot off the line. Jack Grealish took the ball in space in the area at one point, coiled for shot, then passed backwards, which will at least help with the completion metrics.

Orient were bright and swift on the break. Sonny Perkins shot just over after a surge down the left, another case of League One players preying on City’s high line with surprising ease. In stoppage time before the break Josh Keeley made a wonderful save, finding exactly the right spot to spread himself and block Omar Marmoush’s close-range finish with his legs and raised arm.

Half-time arrived with a mild sense of disbelief around the ground. City kicked off after the break with a totally rejigged back three of Abdukodir Khusanov, John Stones and Nico O’Reilly. And Keeley continued to act as a one-man lime-green wall, saving from Marmoush, through on goal, with his face. But City equalised on 56 minutes. It came from a quickly taken corner, Grealish funnelling the ball to Rico Lewis, whose shot was deflected in off the back of the crouching Khusanov.

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Orient almost struck back straight away, a set piece from the left deflected just past the post.

Kelman made another half chance for himself, his powerful shot saved by Ortega. De Bruyne came on and was bumped and harried in midfield. And on 79 minutes City finally took the lead.

The goal was made by Grealish’s floated pass into the space behind the defence, and by De Bruyne’s run from the centre, followed by a flicked finish on the run. There were chances for an equaliser at the death, but City held out for a genuinely hard-earned victory.