The "Clásico Regiomontano" will resume on Saturday with the score equal after a physical 90 minutes of play between No. 1 seed Monterrey and No. 7 Tigres.
Maxi Meza of Monterrey gave the visitors the lead in the 35th minute with a long free kick that caught Tigres goalkeeper Nahuel Guzmán off guard.
He was expecting a centering pass rather than a missile on goal. Five minutes after the break, Sebastián Córdova scored the visitors' response by deftly deflecting a cross from Javier Aquino.
Córdova has now scored in each of the Tigres' four playoff games this season, and in minute 60, he had a second goal disallowed for offside.
The hosts controlled the majority of the early possession and were dangerous on a few set pieces, but they were unable to get into the defensive third of Monterrey.
Despite having control of the ball for 65% of the first half, Tigres only managed two shots, just one of which was successful.
After "los felinos" were momentarily rattled by Meza's goal, the Argentine winger launched another free kick, forcing Guzman to make a quick stop.