Miguel Herrera's side slipped to second spot in the Mexican top flight after Raul Jimenez's 14th-minute opener was cancelled out by second-half goals from Oribe Peralta and Mauro Cejas.
America, though, have two games in hand on league leaders Morelia - who accounted for Pumas UNAM 1-0 away.
Mancilla is equal-leader of the golden boot standings with seven goals, tied with Veracruz's Angel Reyna.
Leon had a narrow 1-0 win on the road at Veracruz, leading for the majority after Hernan Burbano's fourth-minute goal.
Queretaro's Luis Lorona fired the only goal in their 1-0 victory at home to Atlante, while Chiapas were 3-0 winners at home to Atlas.
Mid-table Toluca avoided consecutive defeats, as Alfredo Talavera's 90th-minute penalty spared their blushes in a 1-1 stalemate away to Puebla.
