Manchester City's outlay of £950m can't bring instant European success

So even an outlay of £950m, and a willingness to accept the burden of a £194m loss on a single season, is not enough to guarantee a place in the knockout rounds of the Champions League. Not, at any rate, when the subjects of that investment find themselves up against the tactical astuteness and competitive hunger of a side assembled with one 60th of Sheikh Mansour's spending on Manchester City in the past three years.

Aurelio De Laurentiis, the scion of a famous Italian cinema family, is the man who saved Napoli from ignominy. An hour before last night's kick-off, with the tiers of the wonderfully rackety San Paolo stadium already vibrating with the energy of 60,000 fans, the chairman strolled a lap of the pitch, surrounded by photographers and security men, waving to the cheering crowds. Goodness knows how they would have reacted had he tried the same thing after the final whistle, when his players had ensured that their chance of progress to the next round was firmly in their own hands.

City will have to depend on beating Bayern Munich, who defeated them 2-0 in Germany two months ago, while hoping that Villarreal, a side with nothing to play for, manage to frustrate Napoli. On last night's evidence, the chances of success on both fronts must be slim.

Mancini's wisdom in building his side from the back over the past two years, establishing a defensive platform before letting flair and inventiveness have their head further forward, appeared to have been confirmed beyond argument by their form in domestic competition this season, symbolised by that extraordinary 6-1 victory at Old Trafford. Europe, however, is something different, and probably no one knows that better than a man who reached the final of the European Cup as a player before its expansion in 1992-93 and tackled it from another perspective for four seasons as Internazionale's head coach. Last night it was Mancini's defence, so secure against Premier League sides, that again looked fallible against enterprising opponents.

City's defensive insecurities seemed to be rooted in the positioning of Yaya Touré. The Ivorian was to be found not alongside Nigel de Jong in the classic double-pivot formation whose smothering effectiveness earned Mancini so much criticism in his first season, but further advanced in support of the attacking players.

The Premier League leaders made a comfortable enough start, but midway through the half they began to look vulnerable to Napoli's quick-witted opportunism. Walter Mazzarri's side began to create one outbreak of panic after another in City's defence, with Edinson Cavani, Ezequiel Lavezzi and Marek Hamsik breaking forward in a manner very similar to that in which they had caught out their opponents to take the lead during the first match. Two or three chances had come and gone last night by the time Cavani got the slightest of touches with his head to Lavezzi's corner and saw the ball deflect in off Aleksandar Kolarov and Joe Hart.

Mario Balotelli equalised when David Silva's shot was blocked into his path by Morgan De Sanctis, but four minutes after the restart Touré was caught upfield and Andrea Dossena's cross from the left was met by the lithe, lethal Cavani just inside the penalty area with a decisive first-time shot that restored Napoli's lead.

Balotelli had several chances to make a mark on his return to his native soil, but the one he took was not to be enough. It was his ninth goal in his last 10 City appearances, and with City's chances of advancing to the knockout stage imperilled by Cavani's second goal he was shifted to centre forward. Five minutes later, however, City's scorer was shown a yellow card for what appeared to be a wholly pointless piece of dissent, and when Touré played him through with 12 minutes to go, De Sanctis managed to catch his first-time effort from point-blank range. Two minutes later another shot from a promising position was blocked by an outstretched Neapolitan leg, and a final header from Samir Nasri's cross flew narrowly over the crossbar.

Inevitably, given the somewhat equivocal regard in which Balotelli is held in Italy, he was greeted in the San Paolo cauldron by a banner which featured a crude play on his girlfriend's surname, which is just a vowel away from something unprintable in Italian. Another banner hoisted by the home fans promised "90 minutes of fire", but the flares and rockets which greeted the appearance of the teams took a while to be replicated on the pitch. Balotelli made his first intervention in the seventh minute with one of those sudden, percussive drives that can catch a goalkeeper napping. This time, however, his effort flew past the post. There would be better to come, and worse – having been sick on the pitch during the match, after also being sick on Monday but allowed out that evening for a pizza with his girlfriend.

Given that City are competing in the Champions League for the first time, at least in its present form, a failure to make it into the next stage ought not to represent a disaster. But it would be a major setback in the planning for whatever kind of world domination the club's owner has in mind.