After 90 minutes of goalless action, Raul Jimenez scored the game's lone tally early in the first additional stanza. The imposing striker made no mistake from the spot in the 93rd minute after he was on the receiving end of a wild kick to the foot from Herve Bazile inside the box.
It was a cruel end to the tournament for surprise semifinalist Haiti, which put up a commendable fight, even carrying the play as the two sides approached the 90-minute mark in Glendale, Ariz.
The Haitians, who stunned Canada to reach the last four of the competition, struck the crossbar in the waning seconds of extra time, coming within inches of pushing the encounter to penalties.
But Mexico survived, and will now play the winner of Wednesday's semifinal between the U.S. and Jamaica on Sunday at Chicago's Soldier Field.
El Tri's last Gold Cup title came in 2015.
Tata Martino's side will be looking to extend its own record by capturing the continental crown for the eighth time.