Liverpool have been humbled in the opening game of the Champions League with manager Jurgen Klopp calling for major change at the club.
Last season's runners-up Liverpool have had a patchy start to their Premier League campaign and the malaise spread to Europe's top competition.
Piotr Zielinski's early penalty after a handball, Andre-Franck Zambo Anguissa and substitute Giovanni Simeone made the difference in the first half in Italy.
Zielinski grabbed a second goal after the break before Luis Diaz struck for Liverpool and it could have been even worse for the Reds with Napoli spurning another spot kick.
After the game, Klopp was critical of his team and said Liverpool gave up some simple goals.
"It was really tough to take but I would say not that difficult to explain," Klopp told BT Sport.
"Firstly, Napoli played really well and we didn't. That is the first explanation for the defeat. The two penalties we concede, they were both a little unlucky.
"The next two goals we concede are handed to them on a plate. That is not cool and we should have defended better in the first place and, of course, in the last moment as well."
The Liverpool boss added that the team needed a change to kick-start their season in the Premier League this weekend.
"We need to reinvent ourselves," Klopp added.
"There are a lot of things lacking, not in all games but the fun thing is we have to do it in the middle of the Premier League season and a Champions League campaign. We need a set-up to be better in pretty much everything."
Football world reacts to Liverpool humbling
Left back Andy Robertson was left frustrated at the performance, which will see Liverpool fight to win top spot in the group.
"We were miles too open. You can't come to a place like this and not be compact. They were by miles the better team," Robertson said.
"Too many times they had spaces to run at us and cause us problems.
"Unfortunately, we deserved this result,...we have to wake up and quickly because we can't perform like that."
Liverpool great Jamie Carragher labelled the performance a 'shambles' as the football world ripped into a lacklustre performance.
Not seen many half’s worse than this under Klopp.
A defensive shambles. Matip needs to come on for Gomez. #NAPLIV
— Jamie Carragher (@Carra23) September 7, 2022
Liverpool will probably cling to the return of Thiago Alcantara from injury as the sole positive from tonight. But even if he single-handedly solves the midfield issue (and he is certainly good enough to do so), only poor planning can account for his staying fit being so crucial.
— David Lynch (@dmlynch) September 7, 2022
To be slightly serious about Liverpool for a second, what you’re now seeing is what happens when your midfield offers no protection for a defender, even if that defender is as good as Van Dijk.
They get absolutely cooked in transitions and awkward situations
— Casey Evans (@Casey_Evans_) September 7, 2022
Liverpool's net spend in the transfer market this summer is about the same as Chelsea are paying to get Graham Potter out of Brighton... this highlights the challenge Jurgen Klopp faces working with the current Anfield owners #LFC pic.twitter.com/NFSMFa9YZ6
— Kevin Palmer (@RealKevinPalmer) September 7, 2022
Liverpool run out of inhalers
— Ethan Payne (@Behzinga) September 7, 2022
Liverpool look knackered in every area of the pitch. Reckon that second is one of the worst goals I've seen them concede. Everyone terrible for it.
When it's early September, you look exhausted, and you've got loads injured to boot, I'm not sure how you fix that.
— Daniel Austin (@_Dan_Austin) September 7, 2022
Liverpool getting thrashed cheered me up a little lmao
— Conn (@ConnCFC) September 7, 2022
Robbie Fowler: "I'm a massive Liverpool fan, I love Liverpool but it hurt me tonight watching them." [Bt]
— DaveOCKOP (@DaveOCKOP) September 7, 2022
This should be me struggling to make it through 5 aside, not Liverpool players in a Champions League game. Can talk about a hangover from last season all you want but this is just embarrassing. https://t.co/RaALRS3JYU
— Leanne Prescott (@_lfcleanne) September 7, 2022
— Chris Williams (@Chris78Williams) September 7, 2022
Saved by Alisson!!! Liverpool in shambles.
— George Chomakov (@chomakovg) September 7, 2022
In other results, Ajax overpowered Rangers 4-0 in the other Group A opener in Amsterdam.
Barca beat Czech champions Viktoria Plzen 5-1 at Camp Nou on Wednesday night while Leroy Sane also shone as Lewandowski's former club Bayern Munich won 2-0 at Inter Milan.
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