At least Mario Balotelli still thought this was a fixture worth attending. The Manchester City striker was back at San Siro once again for the Milan derby on Sunday, but that was more than could be said for many others. Despite the stadium's capacity having been reduced for maintenance work, almost 4,000 tickets went unsold. Even the Milan owner, Silvio Berlusconi, decided to pass up the occasion in favour of Vladimir Putin's 60th birthday celebrations.

To put that into context, the corresponding fixture last season sold out with more than a week to spare. This one only got close on the back of a late sales push. As of Wednesday morning there had still been 20,000 tickets available, before the Milan captain Massimo Ambrosini made the first of a series of impassioned pleas by players for fans to get behind the team. "A derby without you is pointless," he said.

The reluctance of many Milan supporters – the Rossoneri were the nominal 'home' team this weekend – to engage was understandable. Punters' purse strings have been tightened as a result of economic tough times, and following the summer departures of Zlatan Ibrahimovic, Thiago Silva, Clarence Seedorf, Antonio Cassano et al this was hardly the sort of vintage Milan side to tempt you to loosen them. In four previous home games this season, they had three times failed to score.

And yet, as kick-off approached on Sunday the old feelings began to resurface. For all the empty seats, there were still more than 70,000 in attendance at San Siro. The noise inside the stadium was still deafening, and the pre-match fan choreography breathtaking. In Milan's Curva Sud an enormous devil throttled a blue-and-black snake. Inter's fans responded with a simple but effective "Ciao merde" – "Hello shits".

That message was soon replaced by something rather more grand, a gigantic 'postcard' made up of four vignettes purporting to tell the tale of the summer. They depicted Silva, Ibrahimovic and Leonardo stood together under Paris Saint-Germain's banner; Cassano shovelling manure in front of Adriano Galliani; a reminder that "you all serve Silvio [Berlusconi]"; and a line of Milan fans queuing up to cancel their season tickets.

As readily as the home support laughed off that display, one or two might have begun to rue even their single-match ticket purchase when Walter Samuel headed home Inter's opener within three minutes of kick-off. If ever there was a bad luck omen for the Rossoneri, this was it. Samuel had already won all nine of the Milan derbies he had started to this point of his career.

The nature of the goal was all too predictable. The Milan goalkeeper Christian Abbiati informed reporters on Saturday that his arms were still sore from parrying Hulk's ferocious shots during their midweek Champions League win over Zenit – yet while his saves from the Brazilian were indeed remarkable, the goalkeeper had also in that game reminded observers of his greatest weakness: an inconsistency in dealing with crosses.

Just as he had misjudged the flight of the Hulk corner which led to Roman Shirokov's temporary equaliser for Zenit, so he made a similar error on Sunday, losing track of Esteban Cambiasso's free-kick as it arced across his area. Samuel's header became the seventh goal Milan had conceded from a set-piece this season.

Abbiati was guilty of a more blatant blunder moments later, passing the ball straight to Diego Milito on the edge of the 18-yard box only for Philippe Mexès to rescue him with a vital sliding challenge before the striker fluffed the rebound. If that was an individual error, then Abbiati might be excused at least some mistakes on the grounds of an inconsistent supporting cast. This was Milan's ninth different back four in as many games.

Both teams, indeed, had lined up for this fixture in formations very different to those envisioned at the start of the season. Massimiliano Allegri, previously committed to a narrow 4-3-1-2, had recently altered to a 4-2-3-1 with Bojan Krkic leading the line ahead of Urby Emanuelson, Kevin-Prince Boateng and the in-form Stephan El-Shaarawy. Inter's Andrea Stramaccioni, meanwhile, had successfully shifted his team in recent games to a three-man defence.

If Inter seemed the more settled in their system then it was Milan who began to take charge as they grew into the game. In the 39th minute Riccardo Montolivo volleyed home an equaliser from outside the box, only to discover that the whistle had already gone for a nonexistent foul by Emanuelson on the Inter goalkeeper Samir Handanovic. Moments into the second half, Inter's Yuto Nagatomo was sent off for a second booking.

The pressure continued to mount: Bojan losing his footing as he closed in on a rebound with Handanovic stranded, before the substitute Giampaolo Pazzini arrived fractions of a second too late to jab home a cross at the far post. Inter, having retreated into a 4-4-1 following the red card, clung on with great determination but not without lapses. Milan appealed furiously, but in vain, for a penalty when Samuel blocked Robinho in the area late on.

At the final whistle Stramaccioni ran to Inter's supporters in the Curva Sud, a celebration with echoes of José Mourinho from a manager who has firmly, repeatedly and with great justification – given their respective CVs – rejected any comparisons to the Portuguese. "I am a nobody and I have not done anything," he reiterated afterwards. Sadly his team's owner is rather less level-headed.

"When I entrusted the team to Stramaccioni, I did so because he has an intelligence which made him resemble Mourinho," said the Inter president Massimo Moratti, whose decision to make the manager's appointment permanent last year was greatly influenced by a 4-2 win in his first derby. "The thing which they have in common above all is that they are both great workers."

The press reaction to the result was similarly hyperbolic. "Whoever wins, turns the corner," Gazzetta dello Sport had promised on the morning of the match, a thesis which was readily confirmed even in the wake of a win that was hardly emphatic. "Inter are in the running for the Scudetto," wrote Jacopo Manfredi for La Repubblica after the game. "Milan are further still from the Champions League."

It is far too early for such judgments, but the suggestion that Inter – roundly criticised in the wake of home defeats to Roma and Siena – have been transformed overnight into title contenders feels especially premature, even if they do remain within four points of the leaders Juventus. Milan, have time yet to improve, but it is true that 12 points represents their biggest-ever gap to first place after seven games of a Serie A season.

What will hurt their fans is seeing Cassano thrive, with four goals and an assist already this season, for their neighbours, while their own attack struggles. The forward was subjected to some venomous abuse on Sunday, with one of the more dark banners reading: "Cassano, play with your heart". The middle letter of the latter word had been replaced with a sketch of a breaking heart, a pointed reference to the player's surgery last year.

It will not have escaped the attention, either, that Ibrahimovic scored twice for his new employers on Sunday night. "We played very well and created lots, without managing to score," insisted Allegri – who laid the blame for his team's defeat squarely with referee Paolo Valeri – but that in itself is part of the point. While El Shaarawy had been in superb form in the lead-up to this game, scoring five goals in his previous four matches, it would be asking an awful lot of an 18-year-old to pick up the slack left by Ibra's departure.

Alexandre Pato did make his return from injury this week, scoring two in a reserve match on Saturday, and were he to finally stay fit for a prolonged period, the Brazilian would make a most welcome addition to Allegri's forward line. Past experience, though, would suggest that cannot be counted on. In the end Milan's greatest mistake on Sunday might have been allowing Balotelli to leave.

Talking points

• Antonio Conte's suspension was reduced from 10 months to 120 days on Friday, a verdict which allows the Juventus manager to return to the bench for his team's game against Palermo on 9 December. Although the manager has not commented on the decision, both his lawyers and the Juventus president Andrea Agnelli made it plain that remain deeply dissatisfied even with this shortened suspension – since they maintain Conte to be innocent of any wrongdoing.

• In the meantime, Juventus endured a fraught weekend – allowing an early lead to slip against Siena and several times in the second half threatening to give away a second goal before Claudio Marchisio finally put them back in front with an expert volley. This team may need to be rotated more thoughtfully going forwards in order to preserve the energies of key players, though one of those thought to be most in need of a rest – Andrea Pirlo – provided the moment of the match when he opened the scoring with a free-kick that slipped under the wall. He had scored with a similar low effort against Roma in the previous league game, though that strike actually went around the defensive line.

• Speaking of Roma, they recorded their first home win of the season, Michael Bradley marking his debut with a goal in a 2-0 win over Atalanta. But rather than resolving the problems which led to the manager, Zdenek Zeman, arguing with the team's vice-captain, Daniele De Rossi, following last week's defeat to Juventus, this result seems likely only to exacerbate them. De Rossi was among a group of senior players – also including Pablo Osvaldo – left out of the starting XI. "For me the hierarchy is established not by surnames but by work," said Zeman afterwards. "They did not show me in the week that they had the right desire. I hope that will change, otherwise it will be difficult for me to use them again."

• Napoli remain level with Juve at the top of Serie A after a 2-1 win over Udinese, Marek Hamsik and Goran Pandev continuing to show themselves capable of providing the goals on Edinson Cavani's off-nights. Lazio, too, seem to have shaken off their mini-blip, Miroslav Klose's goals helping them making short work of Pescara.

Results: Catania 2-0 Parma, Chievo 2-1 Sampdoria, Fiorentina 1-0 Bologna, Genoa 1-1 Palermo, Milan 0-1 Inter, Napoli 2-1 Udinese, Pescara 0-3 Lazio, Roma 2-0 Atalanta, Siena 1-2 Juventus, Torino 0-1 Cagliari.

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