In the 85th, Napoli defender Kalidou Koulibaly picked up his second yellow for tripping Eder, who had already dribbled by another defender.
"We put on a great performance and we were completely superior," said Sampdoria president Massimo Ferrero, who was chewing on his club scarf in anguish after Napoli's goal. "We deserved three points. But that's football. I'm going home with a near heart attack."
Sampdoria has also drawn with AC Milan and Roma this season, and clearly has designs on a spot in Europe.
Ferrero deflected reports that former Italy forward Antonio Cassano could join Sampdoria in the January transfer window.
"I wish him very well but you'll have to ask him," Ferrero said.