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This was a story of two clubs on very different trajectories. Chelsea look every bit Premier League title contenders while Arsenal look short on direction and on the verge of another crisis.
With trips to West Brom in the Carabao Cup on Wednesday and Manchester City on Saturday, Mikel Arteta could head into the international break with more pressure on his shoulders than at any point of his Emirates reign.
So whereas Lukaku has provided Chelsea with a focal point — Arsenal are pointless. Literally.
Defeats against newly promoted Brentford and the Champions League winners prove they are equally adept at losing to teams on either end of the spectrum. Which is why a trip to the Hawthorns could be tense.
But they will not be the only team given a going over by Lukaku this season. The £97.5million striker needed only 15 minutes to show why Chelsea made him a club-record signing, with his opening goal representing an immediate change of style to Thomas Tuchel's attack.
He is precisely what they missed last season and is precisely why they should now be considered the principal challengers to City's crown.
There was a sweet irony that shortly after Lukaku's former club Manchester United toiled to a 1-1 draw at Southampton, he was providing the cutting edge for Chelsea.
And his return to Stamford Bridge could come back to haunt Ole Gunnar Solskjaer, who has his own designs on the title, but considered Lukaku surplus to requirements at Old Trafford.
Pablo Mari will not soon forget this encounter with the 28-year-old, who bossed the Arsenal centre-back.
As a battle of strength, it was not a fair contest, as perfectly demonstrated by Lukaku's goal.
With his back to goal on the edge of the area, it was all Mari could do to see daylight, let alone try to get round his man. Lukaku held him off with ease before laying the ball off and spinning goalwards. As a footrace there was no stopping him, with Mari sent tumbling in his desperate attempt to keep up. It meant Lukaku was left free in the six-yard box to tap in Reece James' cross.
But for Bernd Leno, he would have doubled his tally in the second half when his header was brilliantly pushed on to the bar. And but for better delivery from his team-mates, he might have really punished Arsenal.
This was Lukaku after less than a week training with Tuchel. Chelsea are still to learn how to best exploit his movement and link-up play. Only twice did they find him in the box — and he responded with a goal and an effort that drew a wonder save.
Chelsea are not used to playing with a centre-forward of his calibre — one that makes things happen by the panic he creates in the box.
In time Hakim Ziyech, Mason Mount, Kai Havertz et al may start to play more percentage football because Lukaku is a striker who gambles. Put the ball in the danger zone and he will more than likely be there to finish it.
The type of precision required last season, as Tuchel toiled without an effective No9, is no longer necessary with Lukaku in the team. He will speed up their play — allow them to be more direct on the counter.
Arsenal can point to mitigating factors. James, who scored Chelsea's second, later made contact with Bukayo Saka in the box but no penalty was awarded.
Rob Holding headed narrowly wide in an encouraging second-half response. And Arteta was without a host of players due to Covid and illness. But the sense is those factors only mask deeper-rooted issues.
Against Chelsea they got up close and personal with a club primed for success. Arsenal feel a long, long way from that.