Atalanta has failed to close the gap on Serie A league leaders Juventus when they drew 1-1 with Juventus at Giuseppe Meazza on Friday.
Atalanta wanted a win to keep alive their hopes of winning the title but AC Milan denied them a chance to win the match.
Two first-half goals from either side were enough on the night to share points.
Calhanoghlu fired the home side in the lead in the 14th minute before Zapata equalised for Atalanta in the 34th minute.
Atalanta is on 2nd position with 75 points from 36 games, five less than the points of leaders Juventus who might win the title if they win their next game while AC Milan is on 6th position with 60 points.
25th July fixtures
Brescia vs Parma
Genoa vs Inter Milan
Napoli vs Sassuolo
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