Napoli was jeered off the field after it lost 2-0 at home to Lazio on Saturday -- a result that saw Inter Milan take a huge step toward winning the Serie A title next week.
Matteo Cancellieri and Toma Basic scored for Lazio, which could have won by a greater margin had it not been for a saved penalty and several other missed opportunities.
Inter can now claim the league crown if it wins at Torino next Sunday and Napoli fails to beat lowly Cremonese two days earlier. AC Milan could still delay Inter's celebrations, but would need to win its next two matches, at Hellas Verona on Sunday and at home to Juventus the following week.
Inter, which beat Cagliari on Friday, is 12 points above Napoli and 15 ahead of Milan. There are five rounds remaining after this weekend.
Lazio made an aggressive start in Naples and it paid off as the visitors took the lead in the sixth minute when Kenneth Taylor got down the left and pulled back for a relatively unmarked Cancellieri to fire home.
Lazio could have doubled its lead in the 31st minute after Tijjani Noslin was bundled over by Stanislav Lobotka in the area but penalty specialist Vanja Milinkovic-Savic parried the resulting spot kick by Mattia Zaccagni, who then ballooned the rebound over the bar from close range.
After missing other chances, Lazio did get a second in the 57th minute. Nuno Tavares raced down the left and rolled it across toward Cancellieri, who made a mess of it, but it fell kindly to teammate Toma Basic to fire in.
It was Napoli's first Serie A home defeat of the season.
