Tonic start but an old problem re- appears
It's hard to see how Jurgen Klopp could have had a better opening Premier League outing.
He walked away from the Emirates with three points and a clear view of what he must put right.
The fans could see it too. Plainly.
On the front foot, no problems at all. There was a 20-minute spell in the second half when Liverpool were irresistible and exhilarating.
But Klopp must address the fact that Liverpool can be opened up far too easily at the back. It cost the team three goals yesterday and created nervous moments at the end, which were totally unnecessary.
Alberto Moreno is a liability but the main defensive issue is not across the back four but in front of it.
I really like the look of Ragnar Klavan and I'm happy enough with Dejan Lovren. Klopp played James Milner at left-full in the 4-0 win over Barcelona and I suspect he would have done the same against Arsenal if he was available.
For me, the problems begin in front of the two centre-backs. Klopp still has nobody to play the defensive midfield role.
Arsenal controlled the first-half and Liverpool looked ill at ease and vulnerable. But the game turned on a few moments of true genius.
Philippe Coutinho emerged from relative anonymity and with three or four wonderful touches of skill transformed the game from a bit of a struggle for Liverpool to a complete and clinical shredding of Arsenal.
At 4-1, I sat back a bit gob-smacked. What they did in that spell was ferocious and blew Arsenal away.
Coutinho's free-kick just before half-time levelled Theo Walcott's opening goal for the Gunners and opened the door.
It was a spectacular free-kick from distance which seemed to defy physics as well as Petr Cech and opened the door for Liverpool.
Whatever Klopp did in the dressing room kicked it wide open and inspired a wonderful purple patch.
Beautifully crafted goals followed for Adam Lalana, another for Coutinho and a brilliant goal for Sadio Mane.
This lad is unbelievably powerful and with Georginio Wijnaldum offers a new dimension going forward which, dare I say it, reminds me of the way Liverpool were able to gather and feed off momentum when a certain Luis Suarez was at Anfield.
It conjured up thoughts of teams even further back than that; old style Liverpool and made me think even more that Klopp is on track.
Then a mini-collapse. Arsenal were all but dead and buried after Mane's goal and to allow them back into a position where we were sweating about last-minute equalisers or worse was ridiculous.
An ideal wake-up in fact. Klopp and the fans saw the current state of Liverpool, warts and all, at the sun-splashed Emirates and if anyone was tempted to be carried away by the intensity and pace of the attacking play after the break, their bubble was burst by some poor defending.
As far Arsenal are concerned, this is probably the earliest yet that the critics in the stands have started booing Arsene Wenger and I don't think he will survive many results like this one.
I looked at his line-up at the start and it struck me that it might be one of the most unbalanced I've seen in a long time and so it proved to be.
That said, they were decent in the first half and there wasn't much anyone could have done about Coutinho's cracker. Wenger should have been happy enough at half-time.
They folded badly though and while I know Wenger has had problems with injured defenders, it seems like he's always had trouble with defenders. Sad to say, the clamour for his removal will only get louder and louder.
In general terms, the opening weekend of the season told us what we knew. All the big clubs are a work in progress and the smaller operations will make every game difficult.
Leicester City now know what it's like to stand on the starting line as champions and how every team is gunning for you. They fell at the first hurdle and it won't get any easier.
If anyone impressed, it was maybe Jose Mourinho and Manchester United, who hit the ground running and allowed the manager to stand over his boast before the game that his team can win the title.