Sat high in the West Stand, his mobile phone wrapped in what looked like the sort of £6.99 shonky misspelled 'Cheslea' case you might pick-up on North End Road market, Roman Abramovich did not seem pleased with life.

And dischuffed he might well be: for what he had just witnessed was the most comprehensive home league defeat for the club into which he has poured a good billion quid, since going down 0-3 to Sunderland as reigning champions in November 2010.

Chelsea were poor here from very nearly start to finish.

Guus Hiddink said afterwards that defeat was deserved, and there could be few complaints, but defended the honour of players who he insisted were still fighting for the shirt.

That verdict was not shared by the majority of supporters, many of whom decided long before the final whistle that they would allot a similar degree of effort to on-pitch proceedings, and instead head for either the pub or home.

This wasn't a grand exodus, of the sort we saw from the support of the now-relegated Aston Villa a fortnight back, but was a warning sign that should be heeded by those who run the cub.

Chelsea has been promoted to many of the Premier League's international army of new fans as a place where glory happens, and dreams are made: and a slump such as this can cause real damage to the long-term prospects of any club if it is allowed to continue.

On the pitch, the most obvious place to start was with Chelsea's defence: which looked as hapless and disorganised as Abramovich is likely to have ever seen since taking over this club.

The headless-chickens feel that has characterised this back four so often in John Terry's absence continued: and that will surely be the first major problem to solve for Antonio Conte, when he kicks off what looks likely to be Chelsea's post-JT era.

Baba Rahman, who was probably one of the few blameless Blues in last weekend's dismal defeat at Swansea, was a one-man car crash here.

And this illustrated the problem with a number of recent signings: players that look able when challenged at mid-table level, but who are utterly out of their depth even against a tumbling Manchester City side that barely got out of second gear.

Buy mid-table players, and you get a mid-table team: as has been demonstrated this campaign.

For the first goal it was Kevin De Bruyne, a man about whom there will be much talk yet in this piece, who left Rahman standing – before squaring for the lethal Sergio Aguero to score.

Impressed: Kevin De Bruyne

But that was not the sole disaster of the Ghanaian's afternoon by a long way, and one of the few positives of his signing seems to be that the £14m paid for him is surely now unlikely to rise to the reported £22m headline figure 'based upon performance'.

City's second, again created by De Bruyne pouncing on poor Chelsea positioning and ball control, saw 'ghost green' away shirts whip through blue ranks – again for Aguero to finish.

It was all so quick: the sort of thing Chelsea, not so long ago, used to do to other teams.

One wonders when the tables might be turned and Stamford Bridge can start celebrating such rapid destruction of defences again.

De Bruyne, once of this parish, has been highlighted as yet another example of all that is wrong with Chelsea.

But, as Hiddink said after, hindsight is a wonderful thing: and the Belgian never demonstrated anything in a Chelsea shirt that suggested he was any better than the rest of the bizarrely procured loan army, who have come to nought.

The third was pinned by many on Thibaut Courtois: who, with incredible naivety for one supposedly so experienced, pointlessly raised a knee to take out Fernandinho.

Chance: Thibaut Courtois saves this attempt by Manchester City's Samir Nasri

But it was Gary Cahill, whose dereliction of duty further up the pitch seconds earlier set-up the one on one.

Aguero's penalty completed probably the lowest-effort hat trick he will ever claim.

Asmir Begovic, whose first job was to fail to save the spot kick, will get more of the first team action he so desires during Courtois' ban: at Bournemouth, and home to Tottenham.

All of which is about Chelsea's failures in defence – but they brought no more to the party at the other end.

This looked like a team in need not so much of improving but, like the Stamford Bridge plans presently being considered by the local council, completely flattening and rebuilding from the foundations up.

All of which left Manchester City as the first team to complete a Premier League double over Chelsea since Liverpool in 2011/12.

Bournemouth, Liverpool and Leicester could all yet do the same in the smouldering ashes that remain of this season.

Abramovich, still fiddling with that mobile phone up in the gods, may need to make a few calls to Italy: to inform Signore Conte just how big a job he will have to do.