Much-criticised Mauro Icardi missed a penalty as Samir Handanovic s calamitous own-goal ensured that Inter s poor form under Frank de Boer continued with a 2-1 home defeat to Cagliari in Serie A.
Icardi had been blasted in the run-up to Sunday s encounter following comments made in his autobiography regarding Inter s support, with the club s largest ultras faction Curva Nord demanding the striker be stripped of the captaincy.
Inter vice-president Javier Zanetti confirmed before kick-off at San Siro that the armband may well be taken from the Argentine, who did not help his cause with a terrible attempt from 12 yards out midway through the first-half.
Joao Mario s first Inter goal had appeared to cancel out that miss 10 minutes after the interval, with Handanovic also on fine form at the other end.
However, it was not to be for De Boer s out-of-sorts side, who were pegged back in the 71st minute Federico Melchiorri tucking in from close-range before Handanovic bundled the ball into his own net in the closing stages.
The victory lifts Cagliari above Inter in the Serie A standings, having condemned the Nerazzurri to a third league defeat of the season.
In a first-half dominated by Inter, it was Cagliari beaten in all three of their away league fixtures prior to the clash who went close early on, Luca Ceppitelli heading just wide.
Icardi could have silenced his doubters moments later, but an expertly-timed interception from the experienced Bruno Alves prevented the Argentine connecting with Ivan Perisic s pinpoint cross.
After Antonio Candreva had shanked a volley wide, De Boer s side were gifted an opportunity to take the lead 25 minutes in, Icardi winning a penalty, albeit a soft one, after a reckless foul from Alves.
However, though the 23-year-old stepped up to take the spot-kick, he could only drill a low strike well wide of the right-hand upright.
Handanovic came to Inter s rescue with a stunning double-save soon after the restart, denying Melchiorri before parrying away Marco Sau s follow-up effort.
Fabio Pisacane was on hand to thump in the rebound, but the Cagliari defender was correctly flagged offside.
Those saves proved decisive as, from the resulting counter, Perisic teed up Joao Mario, who despite seeing his initial strike saved, managed to smuggle the rebound home from point-blank range.
Cagliari looked for an immediate response, and would have had it if not for another superb Handanovic stop, who somehow kept out Davide Di Gennaro s venomous volley.
Icardi was the villain again for the hosts shortly after, somehow heading wide despite being unmarked on the edge of the six-yard box.
And Cagliari duly made Inter pay, Di Gennaro s pass deflecting through to Melchiorri, who made no mistake with his finish.
It got worse for the hosts with five minutes remaining, Melchiorri having failed to hit the target with a close-range header moments earlier drilling in a cross that Handanovic could only spill over his line as Inter s winless streak in the league stretched to three matches.
Key Opta Stats:
Cagliari are unbeaten in their last four Serie A games against Inter at San Siro (winning twice).
Cagliari have won three Serie A matches in a row for the first time since October 2012.
Inter have lost a match from a lead position for the first time this season.
Cagliari had two shots on goal in the first half, they had nine after the break (six on target).
Mauro Icardi has missed four of the nine penalties he has taken in Serie A and the Coppa Italia. The striker has missed three of his last four penalties in the league.
