For the second Sunday in a row, City made light work of a top six rival, and for the second Sunday in a row it was Sergio Aguero at the heart of it, netting the 11th hat-trick of his Premier League career to move level with Alan Shearer, though he might feasibly have had five.
Chelsea, for their part, were abject in defence and impotent in attack in a defeat that piles the pressure on manager Maurizio Sarri.
Pep Guardiola made three changes to the side that beat Everton in midweek, switching Aymeric Laporte back to the heart of the City defence, with Oleksandr Zinchenko coming in at full back, while Kevin De Bruyne and Raheem Sterling also returned.
It took the home side less than five minutes to open the scoring, as De Bruyne caught Chelsea napping with a quick free-kick, playing in Bernardo Silva, who squared for Sterling to lash home.
They should have had a second moments later when Aguero somehow missed from two yards out with the goal gaping, but he soon made amends with a 25-yard stunner into the top corner that had the Etihad crowd gasping at the big screen replay.
Barkley then aided the Chelsea implosion with an awful header back towards his own ‘keeper that never looked on, allowing Aguero to steal in for his second and City’s third.
And with little over a quarter of the game gone, Ilkay Gundogan added a fourth, side-footing home from just outside the box, with Chelsea’s defence static and Kepa’s low dive questionable.
The Blues genuinely enjoyed the better of the latter stages of the first period, but after the break City stepped into another gear again.
Aguero might’ve had his hat-trick when powering a header from De Bruyne’s cross off the bar, but he didn’t have to wait long, rolling home from the penalty spot after Cesar Azpilicueta had fouled Sterling.
Sterling added his second late on with another trademark back post finish from Zinchenko’s cross, with the goal sending Chelsea tumbling into sixth place, below Arsenal on goal difference.
Their EFL Cup final commitments mean City may well have been usurped by the time they next kick a Premier League ball, but with Aguero & Co. in this kind of form, keeping them off the top will take quite some doing.