Chelsea striker in thick of good and bad
Swansea 2-2 Chelsea
In a sulphurous match when Chelsea should have been out of sight, then appeared to poke themselves in the eye, it was the vision of referee Andre Marriner which ended up being focused upon. Again.
As ever - or at least since he re-found his form, fitness and fire - Diego Costa was at the centre of it all.
But should the striker who so revels in his pantomime-villain status, in his ability to take it to the edge in the pursuit of giving himself an edge, have even been on the pitch when he executed the spectacular overhead kick that salvaged a point for Chelsea?
And even then, was it dangerous play with a high boot?
With Costa already booked for his lunge on Leroy Fer, it was claimed that he dived to try to seek a red card for goalkeeper Lukasz Fabianski . . . but, hold on, Chelsea will understandably argue, Gary Cahill appeared to be fouled by Fer before the midfielder claimed Swansea's second goal, while Jordi Amat should have been sent off for a series of misdemeanours.
Several of those were perpetrated on Costa, who as well as being cautioned himself was also involved in the spiteful incidents that led to yellow cards for Amat, Fer and Federico Fernandez.
Both teams will brood with a sense of grievance, but Chelsea know that they should have won this encounter to maintain their 100pc start to the campaign.
Marriner was at the heart of a decision in the last Premier League match he refereed that has hit City - he did not see Sergio Aguero's elbow on West Ham United's Winston Reid which led to a retrospective three-match ban - and the official's performance will be pored over again; the crimes of the (not so) ancient Marriner, perhaps.
It would be a shame, to be honest. Turn this game another way and it was simply a rip-roaring and superb advert for the topsy-turvy chaotic, full-on emotional rollercoaster that is the Premier League, with one side overrun, dominated, embarrassingly forced into a first-half substitution and change of formation, and almost booed off at half-time, only to overturn logic in two madcap minutes (two minutes and 10 seconds, to be precise) with the other team then desperately fighting for a draw.
So much debate has surrounded Chelsea's decision to bring back David Luiz for £30m after selling the maverick Brazilian to Paris Saint-Germain two years ago, but there was little case for the defence continuing as it is after this.
John Terry departed on crutches after being caught by Fer and appeared to have hurt his ankle, but the real damage was inflicted on Cahill, who appeared uncertain - and maybe distracted by Luiz's return.
His place is in jeopardy, surely, and he was furious afterwards with the officials, while goalkeeper Thibaut Courtois was a bag of nerves.
It appeared a far cry from the well-drilled backline Antonio Conte assembled at Juventus and, with pretty much the same personnel, with Italy, and while he has rejuvenated Costa, Eden Hazard and Oscar, and while he has the insurance of N'Golo Kante, he will be angry that such a key part of his team was so vulnerable.
That looked highly unlikely as this match unfolded with Swansea manager Francesco Guidolin having selected such a defensive line-up that his intention of damage limitation - and the fear of what Chelsea could inflict - was clear, even if it was quickly unpicked.
Chelsea scored first, when a cross by Branislav Ivanovic was only headed up into the air - and then headed up into the air again - by Fernandez as Fabianski dithered. Oscar collected the loose ball and squared to Costa, who slammed a first-time shot into the corner.
The onslaught continued. Guidolin apologised to Neil Taylor as he took the disgusted defender off but he must have felt like issuing a public apology for how his team were set up and performing - while it appeared that the next outcome would be Amat's dismissal as the Spaniard appeared to lose his head.
Still, just as with the Manchester derby the day before, control can flick like a switch in this league, and it happened with a counter-attack as Fer picked out Modou Barrow, who had replaced Taylor. Barrow swept the ball infield towards the onrushing Gylfi Sigurdsson.
It appeared to be too far ahead, but the ball swung away from Courtois, who lunged to bring down the midfielder.
The goalkeeper was booked, not dismissed, with the rules tweaked this season against the 'double jeopardy' of conceding a goal and losing a player.
Sigurdsson took the penalty kick. Somehow Swansea were level. Then they were ahead.
Terry's pass was loose but Cahill was even more lackadaisical with Fer pouncing, bundling him over and running on.
His shot was blocked by Courtois but trickled towards Fer, who forced it home from close range. Cahill was fouled but the goal stood.
It was some turnaround, but Swansea had too long to hold on. Chelsea regrouped, and with Conte making changes had too much firepower.
They drew level as Oscar turned the ball back to Ivanovic, who worked his way into space only for his low shot to spin up off Amat.
Costa executed a superb scissor-kick from the rebound: Kyle Naughton was close, and Costa's boot was near his head, but it was right that the goal stood.