Koulibaly was in action from the start to the finish to help the hosts defeat the reigning Champions League winners at the Stadio San Paolo, thanks to late goals from Dries Mertens and Fernando Llorente.
The Senegal centre-back was impressive in the heart of the Partenopei's defence as Liverpool trio Roberto Firmino, Mohamed Salah and Sadio Mane failed to score.
Koulibaly, who has played in every Napoli match in this campaign, assessed the team's improvement having conceded just a defeat in four outings so far and also revealed his mission for the 2019-20 season.
“I arrived late to pre-season training as I was at the Africa Cup of Nations and Kostas Manolas had joined a new team, so it took us a while to learn how to play together and we conceded a lot of goals, but we’re improving,” Koulibaly said, per Football Italia.
“I try to give 110 per cent to these fans, as they give me so much love and I want to repay them. I throw myself into the challenge for them, as I want to take the Napoli colours to the top, so it fills my heart when they cheer for me.”
On Sunday, the 28-year-old will look forward to helping Napoli extend their winning streak to three games in all competitions when they visit Lecce.