AC Milan, the Italian Premier League leaders, failed to widen the gap between him and his closest chasers after losing to Atalanta by 3-0 at the San Siro.
The difference between AC Milan and second-placed rivals Inter Milan narrowed to two points.
Christian Romero scored the first goal with his head, from a corner kick by Robin Goossens 26 minutes into the match, before Frank Casey dropped Milan’s Josip Ilicic and scored a penalty in the middle of the second half.
Ilicic scored the penalty, before Dovan Zapata added the third goal late.
Inter Milan were just around the corner from catching leaders AC Milan, but ended their match with a goalless draw with Udinese, to remain in second place, just two points behind.
Atalanta, who became the second team to defeat Milan in the Italian league this season, moved up to fourth place in the table.