Match ends, Inter Milan 1, Napoli 0.
Napoli boss Carlo Ancelotti said his team asked three times for their match at Inter Milan to be suspended because of alleged racist chanting, before a last-minute goal gave Inter victory.
Ancelotti claimed Kalidou Koulibaly was targeted at the San Siro, where the Senegal defender was sent off.
Lautaro Martinez scored a 91st-minute winner for Inter, before Napoli also saw forward Lorenzo Insigne dismissed.
"The next time we'll stop playing, even if we lose the match," Ancelotti said.
"What happened today is not good not only for us but also for Italian football as a whole," the former Chelsea boss added.
"I'm very sorry about what happened to Koulibaly. The boy was on edge, he is an educated footballer who was targeted. Despite our requests the match was not interrupted. I'm unhappy because three times we asked for the match to be suspended."
Koulibaly, 27, was sent off after receiving two yellow cards in a matter of seconds in the 80th minute. The first was for a foul on Matteo Politano, the second was for sarcastically applauding the referee's decision.
After the match he posted on Twitter: "I'm sorry about the defeat and especially to have let my brothers down.
"But I'm proud of the colour of my skin. To be French, Senegalese, Neapolitan, and a man."
The mayor of Milan, Guiseppe Sala, apologised to Koulibaly on his Facebook page.
"It was a shameful act against a respected athlete, who proudly bears the colour of his skin, and also, to a lesser degree, against the many people who go to the stadium to support their team and be with their friends."
Napoli's 27-year-old Algerian left-back Faouzi Ghoulam posted a message of support. "It was painful to hear racist chants directed at my brother," his Twitter post read.
"What's left is secondary, only sadness remains."
Insigne was shown a straight red after appearing to gesture towards the referee in the 94th minute.
Napoli's defeat means defending champions and leaders Juventus, who have won the past seven Italian league titles, are now nine points clear of the second-placed side.
Mauro Icardi hit the Napoli crossbar with the game's very first touch, when he shot straight from kick-off.
But Inter, who remain in third place, had to wait until injury time before Martinez found the net with his first attempt on goal, eight minutes after coming on as a substitute.
Earlier on Saturday, as Serie A matches were held for the first time on 26 December, Cristiano Ronaldo scored an equaliser for 10-men Juve as they salvaged a 2-2 draw at Atalanta.
Inter are now five points behind Napoli in third, 14 points behind Juve.
Line-ups
Inter Milan
Formation 4-3-3
- 1Handanovic
- 33D'Ambrosio
- 6de Vrij
- 37Skriniar
- 18Asamoah
- 15João MárioSubstituted forLa Martínezat 83'minutesBooked at 90mins
- 77BrozovicBooked at 29mins
- 20ValeroBooked at 52minsSubstituted forVecinoat 64'minutes
- 16Politano
- 9Icardi
- 44PerisicSubstituted forKeitaat 74'minutes
Substitutes
- 2Vrsaljko
- 5Gagliardini
- 8Vecino
- 10La Martínez
- 11Keita
- 13Ranocchia
- 27Padelli
- 29Chagas Estevao
- 87Candreva
Napoli
Formation 4-4-2
- 1Meret
- 7Callejón
- 33AlbiolBooked at 67mins
- 26KoulibalyBooked at 80mins
- 6Mário RuiSubstituted forGhoulamat 78'minutes
- 8Ruiz
- 5AllanBooked at 56mins
- 17HamsikSubstituted forMaksimovicat 24'minutes
- 20Zielinski
- 24InsigneBooked at 90mins
- 99MilikSubstituted forMertensat 70'minutes
Substitutes
- 2Malcuit
- 9Verdi
- 11Ounas
- 13Luperto
- 14Mertens
- 19Maksimovic
- 23Hysaj
- 25Ospina
- 27Karnezis
- 30Rog
- 31Ghoulam
- 42Diawara
- Referee:
- Paolo Silvio Mazzoleni
- Attendance:
- 63,946
Match Stats
- Possession
- Home50%
- Away50%
- Shots
- Home12
- Away12
- Shots on Target
- Home5
- Away4
- Corners
- Home5
- Away0
- Fouls
- Home12
- Away10
Live Text
Post update
Full Time
Second Half ends, Inter Milan 1, Napoli 0.
Dismissal
Lorenzo Insigne (Napoli) is shown the red card.
Post update
Lautaro Martínez (Inter Milan) wins a free kick on the left wing.
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Foul by Nikola Maksimovic (Napoli).
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Foul by Mauro Icardi (Inter Milan).
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José Callejón (Napoli) wins a free kick in the defensive half.
Booking
Lautaro Martínez (Inter Milan) is shown the yellow card for excessive celebration.
Goal!
Goal! Inter Milan 1, Napoli 0. Lautaro Martínez (Inter Milan) left footed shot from the centre of the box to the bottom left corner.
Post update
Foul by Keita (Inter Milan).
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José Callejón (Napoli) wins a free kick in the defensive half.
Post update
Attempt blocked. Piotr Zielinski (Napoli) right footed shot from the centre of the box is blocked.
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Attempt saved. Lorenzo Insigne (Napoli) left footed shot from the centre of the box is saved in the centre of the goal.
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Attempt blocked. Matteo Politano (Inter Milan) left footed shot from outside the box is blocked. Assisted by Matías Vecino.
Post update
Fabián Ruiz (Napoli) wins a free kick in the defensive half.
Post update
Foul by Keita (Inter Milan).
Post update
Attempt saved. Mauro Icardi (Inter Milan) header from the centre of the box is saved in the bottom left corner. Assisted by Matteo Politano with a cross.
Post update
Corner, Inter Milan. Conceded by Raúl Albiol.
Substitution
Substitution, Inter Milan. Lautaro Martínez replaces João Mário.
Dismissal
Second yellow card to Kalidou Koulibaly (Napoli).