Napoli's title hopes were dealt a severe blow with a 3-0 loss at Fiorentina on Sunday that leaves Juventus with a clear path toward a record-extending seventh straight Serie A championship.
Napoli played most of the match with 10 men after Kalidou Koulibaly was sent off for a last-man foul on Giovanni Simeone, who went on to score a hat trick.
Napoli coach Maurizio Sarri called it his squad's "worst match of the season."
After Koulibaly's red card and Fiorentina's first goal "we were completely lost," Sarri said. "Over the course of the season we've done well to handle these types of problems but today we didn't."
Napoli were left four points behind Juventus with three matches to play — the same gap which existed until the Partenopei beat Juventus a week ago.
Juventus produced two goals in the final four minutes of a 3-2 win at 10-man Inter Milan on Saturday.
However, Juventus will have to overcome an injury to striker Mario Mandzukic, who had 10 stitches applied to a deep cut in his left ankle after getting stepped on by Matias Vecino against Inter.
In Florence, Koulibaly was first shown a yellow and a penalty was awarded since the referee believed the foul had occurred inside the area. But after VAR help, the referee ruled that the foul had occurred outside the area and changed the card from yellow to red.
Simeone, the son of Atletico Madrid coach and former Argentina international Diego Simeone, finished off a counterattack later in the first half by shooting under the legs of goalkeeper Pepe Reina.
Then after the hour mark, Simeone was quickest to a rebound following a corner and scored from close range. He then added another from a counterattack in the 90th, running past a confused Mario Rui for his 13th goal of the season.