Mauro Icardi scored a stunning hat-trick to condemn AC Milan to defeat in a thrilling Derby della Madonnina.
The Inter Milan skipper, who had twice given the home side the lead, converted a 90th-minute penalty at the San Siro to pile the pressure on Milan boss Vincenzo Montella.
Icardi put Inter ahead with a deft 28th-minute finish and then after Suso had levelled with an equally adept finish, dispatched an improvised 63rd-minute volley.
Montella's men thought they had claimed a point when keeper Samir Handanovic could only carry Giacomo Bonaventura's 81st-minute shot into his own net, but Icardi's late heroics after Ricardo Rodriguez had been penalised for a foul on Danilo D'Ambrosio condemned them to a fourth Serie A defeat of the new campaign.
Unbeaten Inter moved into second place as a result of their seventh league win of the campaign, two points behind leaders Napoli and 10 clear of their city rivals after just eight games.
Sampdoria launched a second half blitz to come from behind and beat Atalanta 3-1 at the Stadio Luigi Ferraris.
Trailing at the break to Bryan Cristante's opener, they struck three times inside 12 minutes through Duvan Zapata, Gianluca Caprari and Karol Linetty to claim the points.
Luca Rigoni's strike ultimately made the difference as Genoa won for the first time this season in a five-goal thriller at Cagliari.
Andrey Galabinov handed the visitors an eighth-minute lead which was doubled by Adel Taarabt with 10 minutes of the first half still remaining.
Leonardo Pavoletti hit back for Cagliari three minutes after the restart, but Rigoni's 75th-minute effort was enough to clinch a 3-2 victory after Joao Pedro scored from the penalty spot four minutes later.
Cyril Thereau came back to haunt former club Udinese as they lost 2-1 to Fiorentina.
Thereau, who spent three years at Udinese before moving to Fiorentina in the summer, opened the scoring after 27 minutes from close range and then doubled his tally shortly before the hour.
Samir pulled one back for the visitors with just under 20 minutes remaining, but Fiorentina saw out the remainder of the match to end a three-game winless streak.
Lorenzo De Silvestri scored a dramatic late equaliser to salvage a 2-2 draw for Torino at Crotone.
The hosts led twice courtesy of Marcus Rohden's 25th-minute opener and Bruno Martella's strike either side of Iago Falque's equaliser.
However, De Silvestri's intervention in the second minute of stoppage time ensured that the spoils were shared.
Andrea Poli's opener and an own goal from SPAL's Bartosz Salamon were enough to secure a third successive Serie A victory for Bologna despite Mirco Antenucci's late consolation strike, while Sassuolo and Chievo played out a 0-0 draw at the Mapei Stadium.