Como qualified for the Champions League for the first time in their history on Sunday, the lakeside club being joined by Roma in Serie A's top four as AC Milan imploded in a 2-1 defeat by Cagliari.
Milan's loss left the seven-time kings of Europe out of the top four after a calamitous end to the season.
Juventus also missed out on an eventful final day marred by fan violence that caused their derby at Torino to be delayed by more than an hour.
Como's 4-1 win at Cremonese, who drop down to Serie B, and Milan falling to a shock home defeat was enough for Cesc Fabregas's side to cap their incredible rise from the lower leagues to Europe's top table.
Como will finish the season fourth, two points behind Roma whose 2-0 win at already-relegated Verona ensured third place and an end to their long absence from the Champions League.
Roma have not played in Europe's elite club competition since being knocked out by Porto in the last 16 in 2019, and a top-four finish came following goals from in-form Donyell Malen and Stephan El Shaarawy.
Malen tapped in Paulo Dybala's brilliant low cross which he whipped in after the Netherlands striker's penalty was saved by Lorenzo Montipo, while El Shaarawy sealed the deal in stoppage time of his last match for the club.
But even that achievement pales into insignificance compared to Como, who have never played in European competition in their history and were in the third tier of Italian football when acquired by tobacco giant Djarum in 2019.
Those three results also meant that Juventus will play in the Europa League next season, with the damage done in last weekend's home loss to Fiorentina.
Juve's match at Torino kicked off over an hour late for "public safety" after one of the Turin giants' fans was admitted to hospital following pre-match clashes with rival supporters.
A win for Luciano Spalletti's side would mean a fifth-placed finish, with Milan, whose livid fans protested loudly against owners RedBird before, during and after a humiliating defeat, dropping to sixth.
MILAN DISASTER, CONTE'S FAREWELL
Milan started the day in third and looked set to reach the Champions League when Alexis Saelemaekers scored in the second minute.
But tap-ins in each half from Gennaro Borrelli and Juan Rodriguez left Milan out of the top four and back in crisis.
Milan's form has been dismal since beating champions Inter Milan over two months ago, a derby triumph which looked to have reopened the Scudetto race.
Instead a paltry 10 points from their final 10 matches left Milan, and RedBird, facing a summer which is likely to be full of changes, even if owner Gerry Cardinale seems to have faith with coach Massimiliano Allegri.
Napoli fans said goodbye to Antonio Conte during an uneventful 1-0 win over Udinese which gave their team a final position of second, 11 points behind new champions Inter at the end of the campaign.
Rasmus Hojlund, now a permanent signing after Napoli qualified for the Champions League last weekend, rattled in his 16th goal of a successful first season in Italy.
However it will be a summer of changes in southern Italy with Bologna's Vincenzo Italiano the man most cited as Conte's replacement.
"It's been an honour, really special to coach Napoli... It's been two great seasons, an exceptional experience," said Conte, who is tipped to take charge of the national team.
Napoli's owner Aurelio De Laurentiis has rejected a $2 billion offer to acquire the club from a group of investors led by Underdog Global Partners.
De Laurentiis has enjoyed frequently tense relations with Napoli fans despite being the man who saved the club from bankruptcy in 2004, and who ended a 33-year wait for a league title.
That 2023 Scudetto, one of the biggest stories of the century in European football, was followed up by another last season under Conte who after the match did a lap of the pitch to bid farewell.