Rodrigo Aguirre converted a 94th-minute penalty as America advanced to the Liga MX final with a 4-3 away win over Cruz Azul on Sunday.
After a goalless draw in the first leg, America took a 2-0 lead in the semifinal courtesy of goals either side of halftime from Alejandro Zendejas and Richard Sanchez.
Ignacio Rivero reduced the deficit with a 68th-minute strike, before Ramon Juarez restored the visitor's two-goal buffer by nodding home after Alvaro Fidalgo's corner.
A Gabriel Fernandez header and a stunning long-range effort from Amaury Morales saw the host draw level four minutes from time.
But America refused to surrender and Aguirre held his nerve from the spot after Erick Sanchez was brought down by Carlos Rotondi.
The fourth official added 12 minutes of stoppage time and Aguirre went from hero to villain when he was sent off in the 98th minute for a bad foul on Gonzalo Piovi.
But the Eagles held on to maintain hopes of a third straight Liga MX title and the 16th in its history.
America will meet Monterrey in the two-legged final next Thursday and Sunday.