He is precisely what they were missing.
Precisely what Arsenal did not need to face as they lurch towards their latest crisis. And ultimately he was the difference on a day that threatened to be far more damaging for Mikel Arteta’s side than it turned out – losing 2-0 as the Emirates opened fully to the public for the first time in 533 days.
Spare a thought for Pablo Mari, who was monstered by Lukaku during a torrid opening 35 minutes.
There was no better example of this than when the Belgium striker opened the scoring.
First, he had the strength to hold off the Arsenal defender’s advances on the edge of the box before laying the ball off. And then, as he spun to race towards goal, he sent Mari tumbling as they collided – leaving himself free to convert Reece James’ cross.
That is what Chelsea lacked last season – a focal point capable of bringing team-mates into the game and a decisive finisher to provide an end product to their dominance of possession.
So shaken up was Mari by the experience of trying to keep Lukaku at bay, that he lost his head in the 34th minute – launching into a reckless challenge from behind on the halfway line.
It earned him a booking – and from the resulting free kick, Chelsea doubled their lead, working the ball from left to right, with Mason Mount sweeping a ball to James on the overlap. The wing-back then emphatically finished into the top corner.
At that point, with just 35 minutes gone, it felt the result could be anything. And the home crowd was ready to turn.
The sunlit skies switched to dark rain clouds as a storm passed over as if to mirror the mood on the terraces. That Arsenal managed to keep the score at just 2-0 will be a source of encouragement to Arteta.
A source of frustration was referee Paul Tierney’s refusal to award a penalty despite James sending Bukayo Saka sprawling in the box shortly before the break and VAR reviewing the incident.
Arsenal improved in the second half and had Rob Holding’s header gone the right side of the post, Chelsea’s resolve might have been tested. But this was a game in which Thomas Tuchel’s side did not have to be at their best to see out.
As hugely impressive as Lukaku’s debut was, Chelsea failed to make the most of his movement and darts into dangerous areas.
His link-up play will also improve as those around him provide better angles to exploit. On a number of occasions, the final ball did not match his runs.
He spent much of the game trying to direct his new team-mates from the front, providing precise instructions of exactly where to play the ball. At times his frustration was clear as they failed to find him. That will come.
Of the two clear-cut opportunities he was provided with, he scored one and forced a stunning save from Bernd Leno with the other – the Arsenal goalkeeper pushing his header onto the bar in the second half.
The fear for Premier League defences is that this was just the start for the player Tuchel believes is the final piece of the puzzle when it comes to turning Chelsea into genuine title contenders.
James, Mount, Kai Havertz, Timo Werner et al will have to learn how to play with a marksman of this calibre. He will keep on making the runs – it is up to them to provide the ammunition.
Such was their blunt edge last season that Tuchel was forced to convert Havertz to, at first, a false No9 and then an orthodox. Even still, in none of these roles did the German emulate a centre forward of the quality of Lukaku.
As such, Chelsea will learn to get the ball into the box quicker. They will learn to play more percentage football because his anticipation means they do not have to be as precise as perhaps they felt they had to be last season with a natural finisher to aim for.
Put the ball in the box and Lukaku will make things happen. He will spark panic. He will hurt teams.
Mari may have walked off the pitch a chastened figure – though it must be said he competed manfully after being given a going over in those opening exchanges – but he will not be alone in being dominated by Chelsea’s No9.
By the time the final whistle had gone Lukaku had topped the statistics for most shots (eight), shots on target (two) and touches in the opposition box (11). That is the way to make an entrance – and the tantalising prospect is that there is so much more to come.