One down, two to go in the battle between the Premier League's two best sides and old pals Pep Guardiola and Mikel Arteta.
Arsenal may hold a five-point lead over Guardiola's Manchester City at the top of the Premier League, but it was the reigning champions who won this first bout, ahead of their league meeting in less than three weeks. The two sides meet twice in the league in the second half of the season and Guardiola will be hoping this defeat will knock Arteta and his Arsenal players out of their stride as the pressure mounts in the title race.
The challenge now facing Arteta is to ensure this setback is not allowed to impact on Arsenal's push for a first league title in two decades, with City ready to pounce should they falter. What impact this result will have on Arsenal remains to be seen, but City showed their enduring class to dump the Gunners out of the competition, leaving them to focus on the league and Europa League.
In this meeting between master and apprentice, it was Guardiola who emerged triumphant against his former City assistant Arteta, who tasted defeat domestically for only the third time this season.
Guardiola suggested there could be fireworks on the touchline between him and Arteta, both known for their impassioned and animated conduct during games.
But someone forgot to light the fuse in what turned out to be a tepid encounter that was ultimately settled by a goal from Nathan Ake, the first the defender has ever scored with his right foot.
City boss Guardiola made two changes to the side that beat Wolves 3-0 in the Premier League, Stefan Ortega replacing Ederson in goal and Nathan Ake coming in for Aymeric Laporte.
Arsenal boss Arteta made significant changes to his personnel, six in all from the side that beat Manchester United 3-2 in an epic encounter in the Premier League last weekend.
With Arsenal's next game not for eight days, Arteta's decision to rest the likes of Aaron Ramsdale, Martin Odegaard, Gabriel Martinelli and William Saliba was puzzling, and one that ultimately backfired.
The first chance of the game went the way of the visitors, Takehiro Tomiyasu forcing a fine save from Ortega with a first-time goal-bound effort.
At the other end, Erling Haaland tried an ambitious overhead kick from 25 yards out, after Arsenal keeper Turner had raced from his line to meet the ball, only for Tomiyasu to clear it off the line.
Ortega came to City's rescue again in the 21st minute, stretching out his left arm to palm away an angled effort from Trossard, after a slick move from the Gunners, who switched play swiftly across the pitch.
Four minutes later, Kevin De Bruyne went agonisingly close to opening the scoring with a curling left-foot effort, which had Matt Turner beaten, but flew just wide of his right-hand post.
Leandro Trossard, who caused City's teenage full-back Rico Lewis problems down his side in the first-half, crossed for Eddie Nketiah just after the half-hour mark, but the Arsenal striker could not direct his effort on target.
City suffered a blow in first-half added time, when John Stones was forced off with a hamstring injury, forcing a defensive reshuffle, with Aymeric Laporte coming on.
The breakthrough came in the 64th minute, through Nathan Ake, with only his second goal of the season. Sub Julian Alvarez struck a post with a long-range effort, the ball falling to Jack Grealish.
Grealish drew two players to him by dragging the ball towards the byline, before feeding the ball back to Ake, who steered the ball into the far corner beyond Turner, to settle the tie.
