Club America dropped their first points of the Apertura season when they were held to a goalless draw at Chiapas FC.
Club America won their first five matches of the new campaign but were unable to breach a resolute Chiapas defence at the Estadio Victor Manuel Reyna.
Their lead at the top of the standings was cut to two points after Monterrey edged past Puebla 1-0.
Dorlan Pabon scored the only goal of the game in the 67th minute at the Estadio Tecnologico to secure Monterrey's fourth win of the season.
Fifth-placed Queretaro failed to make up ground on the leading pack when they slumped to a 2-1 defeat to Cruz Azul.
Cruz Azul took the lead in the 10th minute when Rogelio Chavez scored from the penalty spot, but Camilo Sanvezzo levelled for Queretaro on the half-hour mark.
Joao Rojas netted what turned out to be the winner in the 77th minute and there was late drama when Queretaro defender Yasser Corona was sent off with two minutes remaining.
A hat-trick from Matias Alustiza secured Pachuca a 3-1 victory against Atlas at the Estadio Hidalgo.
The Argentinian striker scored in the 44th and 49th minute before notching his treble with a 73rd-minute penalty after Arturo Gonzalez had reduced the deficit for Atlas a minute earlier.