Match ends, Inter Milan 4, Milan 2.
Inter Milan launched a superb second-half comeback from 2-0 down to stun rivals AC Milan and go top of Serie A.
Inter started in third but leapfrogged Lazio and head the table on goal difference from champions Juventus.
Ante Rebic tapped home from Zlatan Ibrahimovic's knockdown and the Swede headed in the second before the break.
But Marcelo Brozovic volleyed in and Matias Vecino stroked home Alexis Sanchez's cutback before Stefan de Vrij and Romelu Lukaku both scored headers.
Antonio Conte's side looked beaten at half-time after a lethargic opening 45 minutes, but responded in sensational fashion in the second period with four unanswered goals.
Both sides hit the woodwork in a thrilling derby, Hakan Calhanoglu smashing the post with a low drive and Ibrahimovic heading against the post late on, while Inter's January signing Christian Eriksen rattled the crossbar with a long-range free-kick.
Milan had been in good form under coach Stefano Pioli, losing just one of their previous 11 league games under the former Inter boss, but their second-half capitulation keeps them in 10th place.
Inter are now unbeaten in 16 league games and host Napoli on Wednesday, before a crucial clash against fellow title challengers Lazio next Sunday.
"It's still very early to talk about something we can only dream of for now," Conte told Sky Italia.
"We can have a dream. It's a very intense period for us coming up and after that we'll have a better idea of our potential and our real capabilities.
"We can't achieve everything from one day to the next, but we are building. These guys proved they have great strength and guts today."
Earlier on Sunday, Simone Inzaghi's Lazio side showed their credentials by extending their unbeaten run to 18 games with a narrow 1-0 win at Parma - former Manchester City striker Felipe Caicedo scoring the winner.
- 6de Vrij
- 37SkriniarBooked at 55mins
- 87CandrevaSubstituted forMosesat 80'minutes
- 8VecinoBooked at 47mins
- 23BarellaBooked at 55mins
- 15YoungSubstituted forBiraghiat 90+5'minutes
- 9LukakuBooked at 90mins
- 7SánchezSubstituted forEriksenat 72'minutes
- 99G Donnarumma
- 12ContiBooked at 79mins
- 7Castillejo AzuagaSubstituted forda Conceição Leãoat 80'minutes
- 79KessiéBooked at 62minsSubstituted forTolentino Coelho de Limaat 81'minutes
- 18RebicSubstituted forBonaventuraat 84'minutes
- 17da Conceição Leão
- 39Tolentino Coelho de Lima
- 90A Donnarumma
- Fabio Maresca
- Shots on Target
Second Half ends, Inter Milan 4, Milan 2.
Substitution, Inter Milan. Cristiano Biraghi replaces Ashley Young.
Romelu Lukaku (Inter Milan) is shown the yellow card for excessive celebration.
Goal! Inter Milan 4, Milan 2. Romelu Lukaku (Inter Milan) header from the centre of the box to the bottom left corner. Assisted by Victor Moses with a cross.
Zlatan Ibrahimovic (Milan) hits the right post with a header from very close range. Assisted by Lucas Paquetá with a cross.
Attempt saved. Nicolò Barella (Inter Milan) right footed shot from the left side of the six yard box is saved in the centre of the goal. Assisted by Romelu Lukaku with a headed pass.
Corner, Milan. Conceded by Matías Vecino.
Attempt blocked. Rafael Leão (Milan) left footed shot from outside the box is blocked. Assisted by Giacomo Bonaventura.
Simon Kjaer (Milan) wins a free kick in the defensive half.
Foul by Romelu Lukaku (Inter Milan).
Offside, Inter Milan. Nicolò Barella tries a through ball, but Romelu Lukaku is caught offside.
Substitution, Milan. Giacomo Bonaventura replaces Ante Rebic.
Foul by Ante Rebic (Milan).
Ashley Young (Inter Milan) wins a free kick on the left wing.
Substitution, Milan. Lucas Paquetá replaces Franck Kessié.
Alessio Romagnoli (Milan) wins a free kick in the defensive half.
Foul by Milan Skriniar (Inter Milan).
Christian Eriksen (Inter Milan) hits the bar with a right footed shot from outside the box from a direct free kick.
Substitution, Inter Milan. Victor Moses replaces Antonio Candreva.