Napoli 3 Chelsea 1: As Andre Villas-Boas will know, for all managers, there is a very fine line between tactical genius and a reckless failure and last night was one of those occasions when he will have known from the moment he submitted his team-sheet to the Uefa official that it could go either way.

Leaving Frank Lampard, Ashley Cole and Michael Essien out of the team in a game that could well define Chelsea's season will be regarded by some as the equivalent of handing in an 11-line suicide note. But it can also be seen as the moment that he asserted his authority over the old regime of Chelsea and told them that, however great the need, he will not simply slip back into the old ways as he tries to forge a new future.

Even if this proves to the decision that causes owner Roman Abramovich finally to run out of patience, at least Villas-Boas can console himself that he stuck to his own principles, whatever the cost. His team have left themselves with a mountainous task to overturn a two-goal deficit against this Napoli team in the return leg on 14 March and their manager has not made life any easier for himself.

Afterwards, Villas-Boas as good as admitted that Lampard and Cole both challenged him over his selection decision at the team hotel yesterday. There is a rift here with the Chelsea old guard that seems beyond repair and that is even before you factor in the operation that John Terry undergoes today. Without him the defence looks vulnerable like never before, something that even Villas-Boas was not about to disagree with.

See Naples and die, they say. It is supposed to be read as an invitation to witness the glories of the old port city at least once in a lifetime but when you have witnessed Ezequiel Lavezzi and Edinson Cavani shred a visiting defence it takes on a whole new meaning.

As patchy as Napoli were in defence they have an attack that could do damage to any side in the Champions League and against Chelsea, who have now gone five games without a victory, they were always likely to cause problems. Gary Cahill made just his third appearance for Chelsea and David Luiz once again played with the casual nature of a man who has just stepped off the beach.

Chelsea have now taken the lead in all four of their Champions League away games this season and failed to win any of them. Their defence was in pieces last night even with Cole on the pitch from the 12th minute when Jose Bosingwa pulled up with a hamstring injury and had to come off.

Instead of Lampard and Essien, Villas-Boas picked Raul Meireles and Ramires. His thinking, he later explained, was that he could use two defensive midfielders to screen his back four but he accepted that, having lost, he was on a hiding to nothing. "Whatever explanation I give you, in the end it would be a fantastic explanation if we'd won the game," he said. "Any explanation is now useless given the result of the game, so there's no point."

It was, given the stage of the competition and what was at stake, a game that was remarkably open from the very start and there were times when Chelsea were clinging on from an early stage. They needed Petr Cech to rescue them on a couple of occasions early in the first half.

Within 10 minutes, Cech had made the first of two big saves of the half when he blocked Cavani's shot. His second good stop was from Christian Maggio, played in by the excellent Lavezzi. Chelsea were fortunate that for all their defensive mistakes, the Italians were just as uncertain at times at the back.

One such occasion gave Chelsea their goal. Didier Drogba won possession and found Daniel Sturridge on the right. His relatively harmless cross was sliced by Paolo Cannavaro and, when it dropped, it fell straight to Juan Mata, who was able to beat goalkeeper Morgan De Sanctis from relatively close range.

Napoli's goals came late in the half but they were a signal of the kind of havoc this team can wreak when given space around the area. The first began with Cavani, who beat Meireles, and fed a short ball to Lavezzi. Cahill was simply not close enough to him and he shaped his shot away from Cech and into the far corner.

Before the second Napoli goal, Ramires wasted a great chance for Chelsea's second. Then Cannavaro surged forward with the ball in the 44th minute and from out on the right side Gökhan Inler hit a cross to the back post. Chelsea's defence had permitted Cavani to run through it and he met the ball at the back post just ahead of Branislav Ivanovic with what appeared to be his shoulder to beat Cech.

There was more possession for Chelsea in the opening stages of the second half and had Salvatore Aronica not got a foot in on Drogba when he slipped behind the Napoli defence just before the hour then they might have sneaked another goal. The problem for Villas-Boas was that every time Napoli got the ball forward they looked as if they might score.

That was largely because of the devastating attacking unit of Lavezzi, Cavani and Marek Hamsik but also the utter lack of confidence in the Chelsea defence. Luiz was found badly wanting for the third goal. From Hugo Campagnaro's clearance he allowed Cavani to get past him and cut the ball back to Lavezzi who swept it in from close range.

Villas-Boas sent on Lampard and Essien and while Chelsea had some moments they never created the intensive pressure that was a hallmark of the club's recent best teams. Cole kicked Maggio's shot off the line late on in the game after Lampard had given the ball away.

The tie is not yet over, Villas-Boas proclaimed after the game and, in an ideal world, he would believe that. But Chelsea have such fundamental problems to solve by the time Napoli come to Stamford Bridge that sounded last night like a hope more than a promise.

Man of the match Lavezzi.

Match rating 7/10.

Referee C V Carballo (Spain).

Attendance 60,000.