Goals from Riccardo Calafori, Kai Havertz and captain Martin Odegaard saw the defending Premier League champions sweep aside Enzo Maresca's new-look team at the Principality Stadium.
Victory will offered a boost for Arsenal after a mixed preseason for Mikel Arteta with new signing Christos Tzolis laying on the assists for Havertz and Odegaard.
Arsenal are expected to bring in at least one more new face before the transfer window closes, but Arteta is also planning several sales.
Brazilian pair Gabriel Jesus and Gabriel Martinelli were both omitted from the matchday squad to face City, with the duo rumoured to be looking for exits, based on concerns over their lack of playing time in the incoming campaign.
However, Arteta was quick to play down those rumours, as he blamed a Premier League rule which only allows nine substitutes to be names as the reason for his call.
"I was really sad to not have their availability. I've been fighting with the Premier League to extend them and accommodate more players in the squad.
"They deserve to be in the squad. Hopefully we can change that rule."