- Tag results for Napoli
Napoli have 47 points from 20 games and are now seven ahead of third-placed Inter Milan who were held to a goalless draw at home by Sassuolo on Saturday.
Napoli's French-born Koulibaly was targeted by monkey noises and racist chants at the San Siro, before being sent off for sarcastically applauding referee Paolo Mazzoleni.
Four Napoli fans were injured and at least three people arrested.
Liverpool vs Napoli: Carlo Ancelotti frustrated as team denied Champions League "cherry on the cake"
In the end, Napoli finished level on points with Liverpool but were edged out on the third tie breaker, goals scored. That meant every point and goal in the group proved to be decisive.
Mohamed Salah's stunning solo effort put the hosts in front 11 minutes before half-time, but Liverpool were nearly made to pay for their profligacy in missing a series of second-half chances.
Ancelotti's team closed the gap on Juventus to eight points after the seven-time reigning champions continued their unbeaten run with a 1-0 win over Inter Milan on Friday.
Carlo Ancelotti's side still needs a point against Liverpool in the final round of group fixtures to guarantee advancement after Paris Saint-Germain beat the English 2-1 in the other Group C match.
The result saw Chievo move onto one point. It has managed four draws all season but was deducted three points in September for false accounting.
Ivorian Christian Kouame had shocked Carlo Ancelotti's side by opening the scoring after 20 minutes in a match which was suspended for 13 minutes around the hour mark because of torrential rain.
Buffon was suspended for PSG's opening three European games for his behaviour and comments towards the referee during Juventus' quarter-final loss to Real Madrid last April.
Napoli, with 25 points from 11 games, move three points behind champions Juventus who host Cagliari on Saturday with Inter Milan a further three points back before their game against Genoa.
Coach Massimiliano Allegri is likely to rotate his squad after Manchester but he will still be unable to call on Sami Khedira, Emre Can and Mario Mandzukic.
PSG are third, a point behind Napoli with a trip to Italy up next before Liverpool visit Paris next month.
The Italian is returning to the Parc des Princes for the first time since his Bayern side were comprehensively beaten 3-0 by PSG in the group stage of last season's Champions League.
AC Milan extended their unbeaten run to eight matches in all competitions as Gonzalo Higuain scored twice in a 3-1 victory over lowly Chievo at the San Siro.