Costa apologises for 'ugly' spitting incident
Cristiano Ronaldo's double - his first goals in Serie A - proved the difference at Allianz Stadium, but it was Costa's awful conduct in the closing stages that will be remembered.
The winger elbowed and headbutted Federico Di Francesco in the build-up to Sassuolo's late consolation, before spitting in the winger's face, and could now face a lengthy ban.
And taking to his official Instagram account, Costa took full responsibility for his actions.
"I want to apologise to all the Juventus fans for this over the top reaction I had during today's game," he wrote.
"I also apologise to my team-mates, who are always by my side, in good and bad times. It was ugly, I am aware of that and I apologise to everyone for that.
"I want to make clear that this isolated conduct has nothing to do with what I've shown throughout my career."
Gostaria de pedir desculpas a todos os torcedores da Juventus por essa minha reação equivocada no jogo de hoje. Peço também desculpas aos meus companheiros de time, que estão sempre comigo nos momentos bons e ruins. Errei feio, tenho consciência e venho me desculpar com todos por isso. Deixo claro que essa atitude isolada não condiz com o que sempre mostrei em minha carreira. Douglas Costa Vorrei scusarmi con tutti i fan della Juventus per questa reazione fuorviante nel gioco di oggi. Mi scuso anche con i miei compagni di squadra, che sono sempre con me nei momenti belli e cattivi. Ero brutto, ne sono consapevole e mi scuso con tutti per questo. Metto in chiaro che questo atteggiamento isolato non corrisponde a quello che ho sempre dimostrato nella mia carriera. Douglas Costa @juventus
A post shared by ⚡️DC11⚡️ (@douglascosta) on Sep 16, 2018 at 9:47am PDT
Ronaldo's first Serie A goal came in fortunate fashion, but lifted a huge burden off the former Real Madrid man's shoulders.
His second was a more typical Ronaldo finish - a driven effort across the goalkeeper - and the 33-year-old took to Twitter to share the joy of finally breaking his Juve duck.
"I am very happy to have scored my first double with the jersey of Juve and especially to have contributed to this important victory of the team," Ronaldo tweeted.
Sono molto felice di aver segnato la mia prima doppietta con la maglia della Juve e soprattutto di aver contribuito a questa importante vittoria della squadra! pic.twitter.com/Hgk1kz0Xww
— Cristiano Ronaldo (@Cristiano) September 16, 2018