In the bright Etihad sunshine, City were ahead after just seven minutes, much to the delight of the capacity shirt-sleeved crowd.
Bernardo, notably coming deeper to collect the ball, started the move just outside his own box, before playing out to the right.
The visitors could have pulled one back when Ederson’s pass on 19 minutes struck Emile Smith Rowe and rolled towards the far post – but thankfully past it and out of play.
Arsenal’s hopes of getting back into the contest all-but disappeared when skipper Granit Xhaka was shown a straight red card on 35 minutes for a reckless two-footed attempt at a tackle on Joao Cancelo.
Within eight minutes of the Swiss midfielder’s exit, City had increased the lead.
Ferran Torres raced forward down the middle of the pitch before finding Jack Grealish to his left – Grealish teased the Arsenal defender as he moved into the box before nudging the ball cross to Gabriel Jesus who swept home from a few yards out.
The rout continued with a fourth six minutes after the re-start.
A neat passing move on the edge of the Arsenal box ended with Torres teeing up Rodrigo who caressed a low shot into the bottom right corner, leaving Mikel Arteta’s side with more than half-an-hour still to play.
There could have been more, but the champions declared at five as the City fans went through a list of greatest hits with Pablo Zabaleta, Yaya Toure and Mario Balotelli chants echoing around a very happy Etihad.