Liverpool were swept away by a whirlwind first-half performance at the Stadio Maradona from Napoli, who were deservedly three goals to the good at the break.
Piotr Zielinski got the ball rolling from the penalty spot in the fifth minute and two more beautifully worked strikes from Andre-Frank Zambo Anguissa and Giovanni Simeone on his Champions League debut left Jurgen Klopp's side staring at a humiliating defeat.
Poland midfielder Zielinski then added the fourth almost immediately after the restart to ensure Napoli got off to a dream start to Group A.
"It looks like we have to reinvent ourselves," Klopp told BT Sport.
"There are a lot of things lacking. The fun part is we need to do that in the middle of a Premier League season and a Champions League campaign.
"We were not working as a team. We don't play good enough that's clear, that's obvious and everybody sees it.
"We play in the strongest league in the world and have a strong Champions League group but that's the job to do.
"It's my responsibility. I need time to think about it, it's my job to find it out and we have to reset and go," he added.
"In three days we play against Wolves and when they saw the game tonight they cannot stop laughing and think it is the perfect moment. I would think it is the perfect moment, but we have to try to find a set-up to be much better in everything."
Luciano Spalletti's team, who are back in Europe's top competition after a two-season absence, are second but level with Ajax who performed a demolition job of their own against Rangers.
Napoli built on a strong start to their domestic season which has them second after five games in Serie A and will be encouraged by strong performances from new arrivals, in particular firecracker winger Khvicha Kvaratskhelia.
Georgian Kvaratskhelia has already won over Napoli supporters with his exciting wing play and eye for goal, and although he was only on the field for less than an hour he did considerable damage.
Liverpool meanwhile are kept off the bottom by the Scots and now turn their attentions to trying to improve on seventh place in the Premier League.
"We're miles too open, you can't come to a place like this and not be compact," Liverpool's Andy Robertson said.
"When you are a team that presses and you miss one challenge you need someone to follow it up and back his mate up.
"But too many times they got turned and had big spaces to get in behind us and caused our centre-backs problems where it was two against two or three against two.
"Away in a Champions League game you can't defend like that. We have to get back to basics and be compact."
Napoli blow away Reds
Backed by a typically raucous crowd, Napoli came haring out of the traps and could easily have been ahead with less than a minute on the clock.
The lively Victor Osimhen broke onto a long ball from Giovanni Di Lorenzo and nudged it past the onrushing Alisson Becker, but took the ball too wide and instead of trying to lay up his arriving teammates shot off the near post.
They were deservedly ahead shortly afterwards when James Milner handled Zielinski's low shot and allowed the Pole to rifle home the opener.
Napoli would have been further ahead had Osimhen taken a leaf out of Zielinski's book in the 18th minute, but instead he wasted his chance from the spot with a fancy run-up after an on-field review of Virgil van Dijk's clumsy challenge on the Nigerian by referee Carlos del Cerro Grande resulted in another penalty.
However Liverpool were a shambles at the back, constantly caught napping on passes over the top and bewildered by Kvaratskhelia, whose 28th-minute shot was kicked off the line after Osimhen nicked the ball away from Joe Gomez.
And three minutes later Anguissa gave the hosts a lead which more reflected the run of play.
The Cameroon international played a simple one-two with Zielinski to find himself all alone with Alisson before rolling in the second, and from there Liverpool collapsed.
A dream opening half ended with Simeone in tears after making it three just seconds after replacing injured Osimhen, tapping in a simple finish after the irrepressible Kvaratskhelia caused more havoc on the left flank.
Simeone then turned provider for Zielinski to ensure it was a memorable night for the hosts a minute after the break, a first effort denied by Alisson before a follow-up finish was dinked over the Brazilian.
Luis Diaz pulled one back two minutes later but it was all the Reds could conjure up as Napoli shut up shop and saw out a memorable win.
