Monterrey and America are the only Liga MX teams left with perfect records after narrow wins on matchday two.
Both teams needed late winners to move onto six points early in the Apertura season.
Former Valencia attacker Dorlan Pabon netted a 90th-minute winner in Monterrey's 1-0 victory at Pachuca.
He beat a defender down the right before surging into the area, assessing his options and firing a shot in off the post from a tight angle.
At America's Estadio Azteca, where the hosts won 2-1, the visitors took a 20th-minute lead when Juan Arango drilled in a penalty.
Raul Jimenez chipped in an equaliser in the 68th minute after being played in behind.
Pablo Aguilar scored a dramatic winner in the sixth minute of additional time as his header from an impossible angle hit the legs of substitute goalkeeper Manuel Lajud and found the back of the net.
Leon, winners of both the Apertura and Clausura last season, suffered their second loss in as many matches.
Hernan Burbano netted a brace in Tigres UANL's 4-2 win at home to Leon.
He opened the scoring from 25 yards as his strike bounced awkwardly in front of goalkeeper William Yarbrough, who was unable to keep it out.
Burbano finished a goalmouth scramble in the 23rd minute to make it 2-0.
Jose Cardenas' run from midfield and neat finish dragged Leon back into the match just before the half-hour mark.
Tigres deservedly restored their two-goal lead when Emanuel Villa headed in to make it 3-1 before half-time.
Mauro Boselli pulled a goal back for America before the hour-mark, but the hosts sealed the win with Juninho's tremendous 30-yard free-kick.
Former Mexico striker Cuauhtemoc Blanco, 41, made his first Liga MX appearance in six years as Puebla drew 0-0 at home to Veracruz.
Elsewhere, Atlas recorded a 2-0 win at Morelia and Santos Laguna drew 1-1 at home to Cruz Azul.
Chiapas beat Toluca 2-1 as both teams were reduced to 10 men and there were also two red cards in Guadalajara's 1-0 win at Pumas UNAM.
Queretaro were 1-0 victors at Universidad Guadalajara.