Napoli conceded top spot in Serie A to red-hot Atalanta on Sunday (Dec 8) after falling to a 1-0 home defeat to Lazio and dropping to two points from the summit.
Fiorentina earlier remained on Napoli's heels after their 1-0 home win over Cagliari in their first league match since midfielder Edoardo Bove's sudden collapse last weekend.
In soaking wet Naples, Gustav Isaksen stunned the home fans with a brilliant strike, which rifled past Napoli goalkeeper Alex Meret and kept Lazio right in a crowded league title race.
Marco Baroni's Lazio are fifth but only three points behind new leaders Atalanta, who sit top of the pile thanks to a club record-equalling ninth straight league win over AC Milan on Friday.
Fiorentina are, alongside third-placed Inter, level on 31 points with Lazio after they edged past Cagliari earlier on Sunday.
