Gonzalo Higuain hit his 30th Serie A goal then saw red as Napoli's hopes of a first title in 26 years were dealt a blow in a bad-tempered 3-1 defeat to Udinese.
Napoli, who last won the title when Diego Maradona played his penultimate season at the club in 1990, were left with a six-point deficit to Juventus after the champions' 1-0 win over Empoli on Saturday.
Trailing 2-1 at half-time thanks to a Bruno Fernandes double which included a spot-kick and a spectacular overhead kick, Napoli failed to recover after falling behind to Cyril Thereau’s strike just before the hour.
Having seen coach Maurizio Sarri sent from the touchlines before the interval for protesting a second penalty award, Napoli suffered another blow when Higuain was given his marching orders in the final quarter hour.
After an angry exchange with the match referee, the Argentine striker had to be restrained by teammates as he tried to remonstrate with Udinese players.
Read more: Mario Mandzukic header the difference as Juventus defeat Empoli to stretch Serie A lead
If Napoli fail in their title bid on the final matchday on May 15, this loss will be seen as the turning point.
Napoli’s first reverse since a 1-0 defeat to Juventus two months ago leaves them second at six points behind four-time consecutive champions Juventus with seven games remaining. But Sarri was defiant: “We can’t take anything away from Udinese, they played great while we just never got to play at our usual level.
“The defeat will make us angry for a day or so, but it will also give us enough fuel for the next seven games.
“We’re having a great campaign. We have to pick ourselves up as soon as possible.”
Juve’s win on Saturday prompted coach Massimiano Allegri to proclaim: “I hope Napoli drop points.”
His wish was granted as Udinese proved too good for their high-flying opponents, and Gigi De Canio, their coach, said they had always been confident that they would have a chance of taking the three points.
“We didn’t turn up here just to make up the numbers,” he said. “It was a great performance against a top side, and one that should give us the belief that we can do it again.”
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