Franca Jara's second half goal saw Pachuca earn a small advantage at the expense of Monterrey with a 1-0 win at the Estadio Hidalgo in the first leg of their Liga MX final clash.
Edwin Cardona had an early sight of goal but there was an even better chance for Omar Gonzalez at the other end when Jonathan Orozco was forced to get down and push wide.
Orozco had to make a another great save to deny Franco Jara moments later as Pachuca threatened to take the lead before the break.
At halftime, though, Pachuca were forced to make their first change when Colombian defender Oscar Murillo was forced off through injury.
The tension grew by the second half, and Jonathan Urretaviscaya looked to have earned Pachuca a penalty when his shot was blocked by Efrain Juarez's hand, only to have the referee wave play on.
In the 61st minute, Franco Jara headed home to ensure Erick Gutierrez's cross finished at the back of the net to give Pachuca the vital lead.
The Tuzos then pushed intently for a second, with Ariel Nahuelpan coming closest at the death. The Argentine striker forced Orozco to make another excellent save as the game ended in favor of Pachuca.
Both teams will meet again on Sunday at Monterrey's Estadio BBVA Bancomer to determine who will be the next Liga MX champion.