AS Roma's Serie A title challenge all but fizzled out on Sunday when they lost 3-1 to arch-rival Lazio despite being awarded a hugely controversial penalty which overshadowed the game.
Napoli added to Inter Milan's troubles with a 1-0 win at San Siro and Pescara midfielder Sulley Muntari walked off the pitch at Cagliari, saying the referee had failed to act against racist chanting.
Roma were awarded one of the most controversial penalties of the season after Kevin Strootman went down in the Lazio penalty area but replays showed that the Dutchman was not touched by any Lazio player.
Strootman touched the ball once, turned and then fell to the ground although it was not clear whether it was a deliberate dive or he was just trying to get out of the way of a tackle from Lazio's Wallace.
In an incident which will strengthen the case for the introduction of video referees in football, Daniele de Rossi converted the spot kick in the 45th minute to cancel out Keita Balde Diao's 12th-minute opener for Lazio.
Fourth-placed Lazio restored what they saw as justice when Dusan Basta scored with a deflected shot five minutes after the restart and Keita finished off a deadly counter-attack to complete the win with his second goal of the game.
Second-placed Roma's defeat left them nine points behind leader Juventus with four matches to play. Juve have 84 points with Roma on 75, Napoli on 74 and Lazio, virtually assured a place in the Europa League, on 67.
It was Lazio's first league win over Roma since November 2012, a run of seven matches.
Roma brought on 40-year-old Francesco Totti for the final 20 minutes for what could be stalwart's last derby, if he does not renew his contract at the end of the season.
Lazio coach Simeone Inzaghi said referee Daniele Orsato had admitted making the wrong decision during the halftime interval.
Antonio Ruediger completed Roma's misery when he was sent off in stoppage time.
Napoli forward Jose Callejon took advantage of dreadful defending to score two minutes before halftime and extend Inter's winless run to six games. Inter stayed seventh, outside the Europa League places.
[caption id="attachment_60888" align="aligncenter" width="768"]
Inter Milan's Samir Handanovic saves a shot from Napoli's Dries Mertens at San Siro AFP
Relegation-threatened Palermo, who would have gone down if they had lost to Fiorentina, instead earned themselves a stay of execution with a 2-0 win over the Violets.
Alessandro Diamanti put the Sicilians ahead with a free kick in the first half against the run of play and Haitam Aleesami scored the second in stoppage time after a brilliant solo run.
Palermo, one place off the bottom and on their fifth coach of the season, have 19 points, although they are still 10 adrift of Empoli and safety.
Empoli, who are 17th, remained in danger when they lost 3-1 at home to Sassuolo, leaving them only four points ahead of Crotone who held AC Milan to a 1-1 draw.
Marcello Trotta gave Crotone an eighth-minute lead and sixth-placed Milan needed a scrambled goal from defender Gabriel Paletta early in the second half to earn a point.
Chievo won 2-1 at Genoa, Bologna beat Udinese 4-0 and Cagliari beat relegated Pescara 1-0.
After the Cagliari game, Ghanaian Muntari said he had complained to the referee about being racially insulted by fans but the match official instead showed him the yellow card for dissent.
Muntari then walked off the pitch in stoppage time, leaving his side to finish the match with 10 men.
(De Rossi 45-P) Lazio 3
(Keita 12, 85, Basta 50)
(Destro 2, 59, Taider 45+2, Danilo 68-og) Udinese 0
(Pedro 23-P) Pescara 0
(Trotta 8) Milan 1
(Pucciarelli 24-P) Sassuolo 3
(Peluso 20, Matri 34, Duncan 57)
(Pandev 43) Chievo 2
(Bastien 60, Birsa 70)
(Diamanti 32, Aleesami 90) Fiorentina 0
Inter 0 Napoli 1
P W D L GD Pts
34 27 3 4 48 84
34 24 3 7 44 75
34 22 8 4 43 74
34 20 7 7 24 67
34 19 7 8 19 64
34 17 8 9 13 59