A Giovanni Simeone hat-trick sank Napoli 3-0 at Fiorentina as the Neapolitans slipped four points behind leaders Juventus with three games left in Italy's Serie A league.
Juventus, who are seeking a seventh successive Scudetto, won 3-2 at a 10-man Inter Milan on Saturday, a week after Napoli stunned them 1-0 in Turin from a late Kalidou Koulibaly goal to close within one point.
Koulibaly was the villain this time around, with a last-man foul on Simeone earning him a red card in the eighth minute.
It allowed La Viola to take control at the Artemio Franchi and they went in front on 34 minutes.
Argentinian Simeone, the son of Atletico Madrid boss Diego, stormed onto a long ball to fire under Pepe Reina and he again beat the Spanish goalkeeper on 62 minutes, flicking in amid defensive dithering.
He added a third from a Federico Chiesa assist in stoppage time.
"I am still young. I have a lot to learn and improve," 22-year-old Simeone said. "[Coach Stefano] Pioli has always trusted in me. I am happy to be at Fiorentina and I believe in this team."
Napoli coach Maurizio Sarri said that the dismissal and the first goal knocked his squad's confidence.
"I don't know what happened," Sarri said, "because in the past we've always stuck together as a team and fought back. We lost our unity today and let the adversity get the better of us."
Fourth-placed Lazio are four points ahead of Inter and occupy the last Champions League slot after closing the 35th round of matches with a 1-0 win at Torino.
Lazio are level on points with Roma, but trail on head-to-head games.
Atalanta beat visitors Genoa 3-1 to retain sixth place with a one-point lead over AC Milan, who won 2-1 at Bologna.
The Bergamo side had Musa Barrow and Bryan Cristante on target in the first half, with substitute Josip Ilicic sealing the win before Miguel Veloso's free-kick.
Atalanta retain the second of two Europa League berths, while Milan will look to get into next season's competition either by winning the Italian Cup final against Juventus on May 9, or by holding on to their current seventh place in the three remaining games.
If Juve win the cup final then an extra European place is available through the league.
In Bologna, Milan's Hakan Calhanoglu and Giacomo Bonaventura scored before the break and Sebastian De Maio pulled one back for the hosts in the second half.
Sampdoria are level with Fiorentina, three points adrift of Milan, after a 4-1 home win over Cagliari, who had Luca Cigarini sent off and sit two points above third-last.
Relegated Benevento drew 3-3 with visiting Udinese despite the dismissal of Danilo Cataldi. Udinese, with new coach Igor Tudor at the helm, ended a run of 11 straight defeats and sit three points above the three-team drop zone.
Crotone are level on points with Udinese after Marcello Trotta and Simy both netted a brace in a 4-1 home win over Sassuolo earlier Sunday.
Chievo sit third-bottom after losing 4-1 at Roma Saturday and changing their coach.
