Monterrey saw its seven-match unbeaten streak come to an end on Friday at Leon as the club suffered a 2-0 defeat.
Both goals came in the second half and they arrived just five minutes apart as Luis Montes netted the opener before Hernan Burbano doubled the advantage in the 62nd minute.
Leon moves into third place, six points back of leaders Toluca and Tijuana, while Monterrey drops to fifth and is seven points off the pace.
Toluca and Tijuana remained tied atop the league as both recorded away wins on Saturday.
Tijuana held on for a 1-0 win at Queretaro as Alfredo Moreno scored in the first half before Pablo Aguilar was sent off early in the second half for the visitors.
Toluca had an easier time at Atlas with first-half goals from Zinha and Luis Tejada before a stoppage-time strike from Wilson Mathias sealed a 3-1 victory.
Friday's other match saw Jaguares beat Cruz Azul, 1-0, on an own goal from Luis Perea, while on Saturday, America and Morelia finished in a 1-1 draw, Pachuca topped Guadalajara, 1-0, with a second-half penalty kick, and San Luis played out a 0-0 draw at Tigres.
On Sunday, UNAM got goals from Martin Bravo and Eduardo Aguirre in a 2-1 win over Puebla, while Santos handed Atlante its third straight loss, 3-1.