Mauricio Pinilla celebrated in the contemporary fashion. As Inter battled to a 1-0 victory over Milan last October, he cheered, whooped, and punched the air. And then he reached for the nearest internet-enabled device. "#AMALA …!!!" he tweeted – referencing one of his club's most popular anthems. Pazza Inter calls on supporters to always love their team, even though it can be a little crazy.

If anything, Pinilla might be guilty of showing the Nerazzurri too much affection. The aforementioned tweet was not an isolated incident but simply one example chosen out of many. When he is not celebrating Inter's triumphs, Pinilla has also been known to gloat on social media over defeats suffered by their rivals.

Such behaviour might seem normal enough, if Pinilla did not play for a completely different team. The striker did belong to Inter once, back in 2003, joining from Universidad de Chile for a reported €2.5m fee. But after spending his entire first season out on loan – first at Chievo, then Celta Vigo – he was sold to Sporting Lisbon the following summer. Pinilla has played for nine different clubs in the decade since, yet never the one which he professes to love most.

Ivan Zamorano was long held responsible for Pinilla's Inter leanings. The former Chile striker had, like Pinilla, grown up in Santiago, before moving to Europe in pursuit of footballing fame and fortune. In 1998 Zamorano helped Inter to lift the Uefa Cup, scoring their first goal in the final against Lazio. Five years later, he was the one who first recommended Pinilla to the Nerazzurri.

Yet Pinilla himself has insisted that his love for Inter goes back even further. "I have supported them for many years, forever really," he said during one interview back in 2011. "They were the team I followed as a boy – not just when Zamorano joined, but before that, too."

Some might argue that Pinilla was still a boy when he arrived in Italy. Barely 19 at the time, he had already made his international debut for Chile but became distracted by the trappings of celebrity. "I wasn't thinking about football," he would tell Gazzetta dello Sport many years later. "I thought that all you needed [to succeed] was talent. That just isn't the case."

Over the next five years he became more famous for his deeds off the pitch than on it. Wherever he went, Pinilla quickly established himself as a favourite of the local gossip columnists. In 2008, he was infamously hospitalised after getting into a fight with his compatriot Luis Jiménez – himself an Inter player at the time – in a Santiago nightclub.

It is tempting to wonder whether that incident brought on some kind of epiphany. A year later, playing for Grossetto in Serie B, Pinilla made the symbolic gesture of changing his squad number – reversing the No15 he had played with his entire career to instead wear No51. This was a conscious and stated attempt at a fresh start. It worked. Despite injuries, Pinilla went on to score 24 goals in as many appearances.

Such form won Pinilla a move to Palermo, and from there he joined Cagliari in January of last year. In many ways it felt like the right spot. A footballer who had never found a place to settle down in his career had found his way on to a team that would soon also be without a home.

Pinilla was an instant hit, his eight goals in 14 games between January and May helping Cagliari to achieve their highest-ever Serie A points tally. Finally he was delivering as the sort of powerful, explosive forward Inter had once envisaged. Even so, his enduring fondness for the Nerazzurri rubbed some supporters up the wrong way. Many have felt moved to tweet back at Pinilla over the past 15 months, asking where his priorities really lie.

So it was that Pinilla found himself confronted by reporters last week, asking whether he might secretly want Cagliari to lose their upcoming game against Inter in Trieste. Cagliari, after all, had little left to play for this season. Inter were engaged in an increasingly desperate struggle to secure a European place. The player insisted his focus was solely on helping Cagliari to win the game. Even those who did believe him, however, might have been surprised by how far he was willing to go.

The game was still goalless with 28 minutes left to play on Sunday, when Pinilla raced into the box down the left-hand side. As he moved past Matias Silvestre, the Cagliari forward suddenly crashed to the ground – kicking his legs out behind him. The referee pointed to the spot, and Pinilla himself got up to convert the penalty.

Pinilla would add a second before the end, and Inter were fortunate to avoid an even heavier defeat when Victor Ibarbo struck the crossbar with five minutes remaining. But there was no question that the penalty had defined the game. It was far from a clear-cut call. Even after repeated TV replays, it was hard to discern any contact between Silvestre and Pinilla.

The forward's post-game comments did nothing to improve Inter's mood. "I swerved left and as soon as I felt a touch I threw myself down, because a penalty is a penalty," said Pinilla. "When an opponent touches you in the area, an attacker has to be smart enough to understand the game. Am I suggesting you need to dive? No. It's not a dive. When they touch you it's a penalty."

There are those who would laud Pinilla for such honesty, saying that most attackers are of the same mindset, even if they wouldn't admit it. But many others will consider this murky territory. Not all contact between players constitutes a foul, and the suggestion that forwards should be "smart enough" to exaggerate is plainly provocative.

Inter, either way, were left feeling aggrieved. This was the second week in succession in which a questionable penalty was given against them. For a team that was already falling apart under its own steam, the cumulative effect has been devastating. The club's owner, Massimo Moratti, spent the last week questioning the "good faith" of Serie A's officials, and this latest episode will do nothing to improve his mood.

Andrea Stramaccioni attempted to strike a more conciliatory note on Sunday, expressing his frustration with recent decisions but stating the belief that they still amounted to nothing more than simple human error. The manager will be aware, after all, that he has made many mistakes of his own.

Inter have been unfortunate with injuries – losing all three of Diego Milito, Antonio Cassano and Rodrigo Palacio up front – but the manager's decision to send Walter Samuel on as a make-shift attacker for the final 15 minutes against Cagliari smacked of resignation. Stramaccioni had included Francesco Forte, a centre-forward from Inter's youth team, on his bench but lacked the courage to give him a try even in such desperate circumstances.

The manager will know that his hold on the Inter job is weakening. Moratti is extremely fond of Stramaccioni, but his team is now seventh, nine points outside the Champions League places. Inter have lost four of their last five games, as well as 12 overall in the league this season.

Their last chance to salvage something positive from this campaign lies in the Coppa Italia. Inter trail Roma 2-1 from the first leg of their semi-final, but will play the second at San Siro on Wednesday. If the task of overturning that deficit did not seem daunting enough for a team in such shabby form, they must now likely do so without Walter Gargano and Yuto Nagatomo, each of whom left Sunday's game with injuries.

Here too, questions are being asked. While Stramaccioni has repeatedly cited Inter's misfortune with injuries as a mitigating factor for their poor results, more than one newspaper has begun to ask whether the coaching staff might not be complicit in the way that they have handled the players.

The club's directors, meanwhile, are responsible for failing to ensure adequate depth in key positions, most notably up front. There was talk in the January transfer window that the club could even bid for Pinilla, to serve as Milito's back-up. "In recent years I've been close to returning a few times," the player said on Sunday. "But nothing ever happened."

Instead, on Sunday, the Inter supporter hammered two more nails into the coffin of their season.

Talking points

• Juventus will have the opportunity to further extend their lead at the top of Serie A on Monday night after Milan and Napoli drew 1-1 at San Siro. Mathieu Flamini scored and later got sent-off for Milan, while Goran Pandev showed the sort of poachers' instincts that Napoli have missed from him all season with the equaliser. In the end, the greatest talking point might have been Massimiliano Allegri's decision to start Stephan El Shaarawy on the bench. "He needed to recharge his batteries on a physical and mental level," said the manager. "If every player needs to play 50 games, then next year we can just have a squad of 14 players."

• What it all means, of course, is that Napoli remain four points clear of Milan in second place. (They are also, for what it's worth, 15 points better off than at the corresponding point last year.) With the Rossoneri travelling to face Juventus in Turin next week, there may yet be a possibility for Fiorentina (another four points behind) to challenge for third.

• Roma revived their Europa League push with a 2-1 win at Torino – a result that moved them level on points with Lazio. But frankly I'd stop worrying about league tables right now and just enjoy this goal from Erik Lamela instead.

• The Derby della Lanterna ended in a 1-1 draw this weekend, Francesco Matuzalem rescuing a point for Genoa with 10 minutes left to play. The question is, did he mean it?

Stefano Sorrentino commits a goalkeeping blunder for the ages during Palermo's 1-1 draw with Bologna.

• Those two results were both good news for Siena, who blew a two-goal lead away to Pescara on Saturday evening but eventually prevailed 3-2 (albeit with the help of an offside winning goal). Unbeaten in five games, Siena are now two points clear of Genoa and Palermo in 17th place. If the table provides encouragement for a team who began the season with a six-point deduction, then the fixture list is rather less reassuring. Siena still have to visit Roma, Napoli and Catania, as well as facing Milan and Fiorentina at home.

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

Latest Serie A standings.