Fifth-placed Genoa are just a point behind La Viola after they won a bad-tempered city derby against Sampdoria 3-1.
Argentine Diego Milito was the hat-trick hero, but three players were sent off and nine more booked as the game descended into chaos at the end.
AS Roma fell out of the running for a top four finish as they were held 0-0 at home by Chievo, leaving them eight points behind Fiorentina with just four games left.
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