Napoli piled the pressure on Andre Villas-Boas and put one foot in the Champions League quarter-finals with a 3-1 first leg victory over Chelsea at the San Paolo here on Tuesday.
Ezequiel Lavezzi scored a brace and Edinson Cavani added the third after Juan Mata had given the visitors the lead.
Villas-Boas will now face more questions over his future with his side struggling in the league and hanging on in the FA Cup after a fifth round home draw with Championship side Birmingham City.
A 2-0 win at Stamford Bridge in the last 16 second leg in three weeks time would be enough for the Londoners to progress but on this evidence Chelsea don't look capable of keeping a clean sheet against anyone.
The absence through injury of captain and star centre-back John Terry was marked as David Luiz and Gary Cahill were made to look vulnerable and incapable of plugging any defensive gaps.
And with Terry ruled out for the next six weeks as he needs a knee operation -- news that was announced before the game -- Chelsea's defence doesn't look likely to improve any time soon.
But Villas-Boas said he remained confident.
"Firstly it's a negative result of course but one we are sure we can turn around at the Bridge due to the amount of chances we had," he said.
"Being more efficient and clinical was the difference between the two teams, we both had about the same number of chances.
"It was a very open game for the Champions League but Napoli found that efficiency.
"We had chances but we paid a heavy toll with the chances that we created while Napoli made the most of their opportunities when they could."
But that's not to take anything away from Napoli who were scintillating on the counter attack -- as they had been against Manchester City in the group stages -- although only mildly less inept than Chelsea at the back.
"I'm disappointed about the goal we didn't score through (Cristian) Maggio, it would have been an important advantage which we would have deserved," said Napoli coach Walter Mazzarri.
"Now we'll go and play for qualification in what will be a difficult game, we'll have to score in London."
Villas-Boas laughed in the face of his supposedly precarious position by picking a surprisingly attacking line up with Daniel Sturridge, Mata and Florent Malouda behind Didier Drogba.
It made for an entertaining game but Chelsea's defence was too often exposed.
Gokhan Inler released Cavani after just nine minutes with Cahill's slip giving the Uruguay forward time to control and shoot but Petr Cech came to his side's rescue.
The Czech goalkeeper did so again when Lavezzi released the overlapping Maggio inside Luiz.
And yet it was largely against the run of play when Mata gave the visitors a 27th minute lead, helped in no small part by the pitch.
After a neat passing move Sturridge tried to slip the ball inside to the Spaniard.
Paolo Cannavaro was in the way but a bobble saw him slice his attempted clearance up in the air and Mata calmly let it drop and side-footed home from 10 yards.
Luiz then beat goalkeeper Morgan De Sanctis to a Mata corner but headed over.
The leveller came on 38 minutes as Lavezzi sold Raul Meireles a huge dummy, opening up an acre of space outside the box from where he curled a precise finish around Cech.
Brazilian Ramires immediately replicated Lavezzi's feint up the other end but couldn't do likewise with his finish.
And in first half stoppage time Inler stroked the ball to the back post where Cavani got ahead of Cahill to brilliantly improvise by shouldering the ball in from close range.
In the second half an awful mistake from Meireles - who is suspended for the second leg after being booked - allowed Cavani to slip in Lavezzi but the Argentine failed to hit the target.
Chelsea were piling on the pressure but chances for Drogba, Mata, Malouda and Cahill came and went without the home goalkeeper being troubled and they were to pay for their wastefullness.
The third Napoli goal came on 65 minutes as Luiz hesitated under a long punt forward and Cavani nipped in front of him, drew Cech and slid the ball left for Lavezzi to roll the ball past Cahill on the line.
It could even have been worse for Chelsea in the final 10 minutes after Marek Hamsik got in behind the defence and crossed for Maggio but Ashley Cole somehow cleared his shot off the line.