A sluggish start from the visitors saw Victor Osimhen almost put the Serie A side ahead after he rounded Alisson before hitting the post, but it was just minutes before they broke the deadlock courtesy of a Piotr Zielinski penalty that was awarded after James Milner's handball.
Napoli were handed a second spot kick after Virgil van Dijk was adjudged to have fouled Osimhen, only for Alisson's stop to ensure the deficit would remain at a single goal. But that wasn't for long after the Reds found themselves 2-0 down when André-Frank Zambo-Anguissa connected with Zielinski's pass, before impressive solo work from Khvicha Kvaratskhelia on the left flank saw him cut back for substitute Giovanni Simeone to add a third for the Naples side before the half-time whistle.
Jurgen Klopp introduced Joel Matip at the break, but that did little to stop the storm as Napoli scored within 90 seconds of the restart. Despite Luis Diaz's quick reply with a fine finish from outside of the box, Liverpool were unable to find their way back into the game.
It's difficult to find positives in a performance that was so one-sided on the night, but Luis Diaz's display is something that stood out.
The left-winger scored yet another goal from cutting in on his favoured right foot, and he was the only player who looked like he could make something happen on the forward line.
Liverpool started the game too slow and couldn't seem to stop a relentless Napoli side. The defending was naive across the match, while there didn't seem to be any structure between the midfield and defensive line. A very poor display from the 21/22 Champions League runners-up.
Manager rating (out of 10)
Jurgen Klopp, 5 -- Fitness problems may have forced Klopp's hand in terms of team selection against Napoli, but his persistence with the high-line is something that may need to be tweaked after how it was exposed.
Player ratings (1-10; 10 = best, players introduced after 70 minutes get no rating)
GK Alisson, 6 -- There wasn't much that the Liverpool goalkeeper could do about any of the goals, having made a number of strong stops. He was simply let down by his defence on too many occasions on the night.
DF Andy Robertson, 5 -- Liverpool's starting left-back took a while to get going but he was one of Liverpool's better players in the second half, as he looked to get forward to combine with Luis Diaz who began to operate more centrally.
DF Virgil van Dijk, 4 -- The Netherlands star has to do much more to help command Liverpool's defensive line as the most experienced player in the side. Jurgen Klopp's side were all over the place at the back, and that left the mountain too difficult to climb in the second half. A clearance off the line denied Napoli in the first half, but he then conceded a penalty.
DF Joe Gomez, 4 -- Nothing seemed to go right for Joe Gomez on the night who was caught in possession on a number of occasions, and in moments where he did make contact, the ball seemed to divert back into a dangerous area. The 25-year-old's positioning also left a lot to be desired. Replaced at half-time for Joel Matip.
DF Trent Alexander-Arnold, 4 -- A well-picked out pass into the feet of Mohamed Salah on the half-hour mark almost saw the Egypt international level the scoring in the first half, but Alexander-Arnold was beaten too easily by Kvicha Kvaratskhelia in the build up for Napoli's third goal.
MF Fabinho, 5 -- The Brazil international couldn't seem to impose himself on the match, with Napoli playing through his press with relative ease. That factor wasn't helped by an overall poor display from Liverpool in midfield as a team.
MF James Milner, 5 -- A handball inside the box from Milner saw Napoli awarded a penalty to edge themselves into an early lead. The experienced midfielder was careless in possession, with many of his long balls easily dealt with by the Serie A side's defence.
MF Harvey Elliott, 6 -- Liverpool's brightest player in midfield as Elliott looked to progress the ball forwards into positive areas. Elliott often made the right decision despite being the Reds' youngest player on the field.
FW Luis Diaz, 7 -- The Colombia international was Liverpool's brightest spark on the night, even in a game that looked far out of reach. His finish outside the box early in the second-half was excellent, while he then came close with a header that was well saved by Meret.
FW Roberto Firmino, 5 -- Liverpool's centre-forward couldn't get into the game and found himself often crowded out by defenders. An almost anonymous display from the Brazil international.
FW Mohamed Salah, 5 -- Salah had Liverpool's only real chance of the first half, but his effort was tame and simple for Alex Meret to save. Napoli kept the Egypt international quiet overall, in a match where he struggled to make an impact from the right wing.
Joel Matip (Gomez, 45"), 6 -- Introduced at the break for Joe Gomez but could have done more for Napoli's 4th goal. Brought the ball forwards from defence well, and was able to break the lines with his passing.
Darwin Nunez (Firmino, 62"), 6 -- Nunez looked to make runs in behind to stretch the play, but Liverpool didn't find him in space enough. The former Benfica forward's decision-making looked to be positive, and he did well to pick out Diogo Jota late-on in the game who couldn't finish.
Thiago (Milner, 63"), 7 -- A return from injury from Thiago saw him add more control to Liverpool's midfield, a factor that was desperately needed after Napoli's continued success. Won the ball back on a number of occasions.
Diogo Jota (Salah, 63"), 5 -- Jota found himself in positive areas but he was quickly crowded out by defenders. Regardless, vital minutes after a return from injury sustained in pre-season will be helpful going forward.
Arthur (Elliott, 77") N/R -- Introduced for Elliott in the 77th minute in a Liverpool debut against familiar opposition for the on-loan Juventus midfielder, and he looked to enjoy his minutes playing alongside Thiago.