Napoli's Serie A title hopes were dealt a potentially fatal blow on Sunday when they slumped to a 3-0 defeat at Fiorentina after defender Kalidou Koulibaly was sent off in the eighth minute and their rivals took advantage with a Giovanni Simeone hat-trick.

The defeat left Napoli four points behind leaders Juventus with three matches to play, only a week after re-igniting the title race with a last-minute win away to the Turin side.

Juventus won 3-2 at Inter Milan on Saturday after scoring twice in the last five minutes.

Koulibaly was dismissed for felling Simeone as he was about to shoot. The referee at first gave Fiorentina a penalty and handed the Senegalese defender a yellow card, but changed that to a free kick for the home side and a red card for Koulibaly after reviewing the incident with the video assistant referee (VAR).