The visitors had the first dangerous chance through Javier López, but his shot grazed the post. Then Chivas was forced into an early substitution after an injury to Jair Pereira saw him leave the game in the 15th minute. His replacement, Michael Pérez, was then called for a foul in the box in the 28th minute, which gave Atlas a penalty kick.
That PK proved to be decisive. Matías Alustiza stepped up to take the kick and he sent it low to Rodolfo Cota’s right to make it 1-0 for the Rojinegros.
Chivas thought they had found the equalizer just minutes later, but Alan Pulido’s would-be goal was disallowed for offside and Atlas took the lead into halftime.
In the second half, Chivas took control of possession as they looked for an away goal. Oswaldo Alanís had a good chance with his left-footed attempt, but his shot was deflected.
At the other end, Daniel Álvarez took the ball into the box but saw his shot saved by Cota.
El Rebaño continued to have more of the ball, but they were lacking a cutting edge. They were unable to turn possession into goals as they fell by the minimum difference in the Estadio Jalisco.
With the 1-0 win, Atlas will advance to the quarterfinals with a win or draw in Sunday’s second leg, while Chivas needs to win to move on; 1-0 would do it, but if Atlas scores, Chivas will need to win by two.
Atlas: Miguel Ángel Fraga, Cristian González, Daniel Arreola, Luis Reyes, Leiton Jiménez, Bryan Garnica, Clifford Aboagye (Jahir Barraza 76′), Daniel Álvarez (Christian Tabó 85′), Javier Salas, Martín Barragán (Luis Robles 62′), Matías Alustiza.
Chivas: Rodolfo Cota, Jesús Sánchez, Edwin Hernández, Jair Pereira (Michael Pérez 15′), Oswaldo Alanís (Néstor Calderón 65′), Javier López (Edson Torres 74′), Orbelín Pineda, Carlos Salcido, José Juan Vázquez, Carlos Fierro, Alan Pulido.