Serie A leader Napoli was eliminated from the Italian Cup after a 2-1 defeat at home to Atalanta on Tuesday.
Timothy Castagne and Alejandro Gomez scored to send Atalanta through to the semifinals, where it will meet either three-time defending champion Juventus or Torino.
It was the first time Atalanta had reached the semifinals since the 1995/96 season, when it went on to finish runner-up for the second time. It won the competition in 1963.
"It was an amazing performance, and a fantastic achievement," Atalanta coach Gian Piero Gasperini said. "Having reached the semifinals by winning at Napoli ensures that our season is already rich ... it's a really important result for us."
Both sides had chances to score in an even first half before Castagne broke the deadlock five minutes after the interval.
Gomez's cross from the left found Andreas Cornelius and his effort came off Napoli defender Mario Rui. But the rebound went straight to Castagne, who slammed the ball home.
Gomez appeared to have sealed the match with a wonderful solo effort nine minutes from time, but Dries Mertens gave Napoli hope three minutes later when he headed in a cross from fellow substitute Lorenzo Insigne at the back post.
Napoli leads Serie A at the halfway stage, with a point more than second-place Juventus.
But it was also eliminated from the Champions League last month.
"We are having an extraordinary season," Napoli coach Maurizo Sarri said. "We have the right attitude in the league but we suffer more in the cups ... certainly we could have done something better in the cups.
"Maybe subconsciously we apply ourselves more in the league."