Free-scoring Atalanta missed a chance to move back into the top four of Serie A when they suffered a shock 2-1 home defeat on Monday against SPAL, who started the day bottom of the table.
Atalanta, the Serie A top scorers with 50 goals from 20 games, had won their last two home games against AC Milan and Parma 5-0 and another comfortable win was on the cards when Josip Ilicic put them ahead after 16 minutes.
Duvan Zapata crossed the ball from the left and the Slovenian flicked the ball into the net with a backheel.
The Colombian also hit the woodwork but there was a warning for Atalanta when Andrea Petagna struck the post for SPAL just before halftime.
SPAL, who were founded by Salesian priests in 1907 and returned to Serie A in 2017 after a 49-year absence, turned around the game in a six-minute spell after the break.
Etrit Berisha ensured SPAL's fourth league win of the season with a fingertip save from Zapata's deflected shot in stoppage time.
Atalanta stayed fifth with 35 points while SPAL, with 15, moved off the bottom of the table where they were replaced by Genoa.