Man City 1-0 Arsenal: Ake knocks Premier League leaders out of FA Cup
In a fourth-round battle between surprise Premier League leaders Arsenal and a second-placed City side who are clinging to their coat-tails in the top flight, it was defender Ake who made the difference on Friday.
He delivered the breakthrough in the 64th minute, with a sharp side-footed finish finding the bottom-right corner, out of the reach of goalkeeper Matt Turner.
The top two have still to meet in the Premier League this season, with this tie a taste of what is to come when those games take place in February and April.
Guardiola's City began strongly, but Arsenal had a big chance in the fifth minute when Takehiro Tomiyasu's powerful strike from just inside the penalty area was palmed away by Stefan Ortega.
Tomiyasu was then on hand at the other end to keep out Erling Haaland after the striker looked to loop an overhead kick past Turner, who had raced off his line to make an interception.
Arsenal's new winger Leandro Trossard was denied by a smart save from Ortega after taking on City right-back Rico Lewis and lashing a left-footed strike towards the far corner.
Kevin De Bruyne sent a curling shot from just outside the penalty area a yard wide of the left post, while City suffered an injury blow just before half-time as John Stones went off with an apparent hamstring problem.
Early in the second half, Turner reacted sharply to push away a low cross from De Bruyne that was intended to tee up Haaland for a tap-in
City introduced Julian Alvarez and Kyle Walker just before the hour mark and began to look sharper. Alvarez went close by hitting the right post, a mere 10 seconds before Ake slotted City ahead with a composed finish.
Arteta called on reinforcements, with captain Martin Odegaard among the players sent on from the Arsenal bench, but the Gunners could not force a replay.