The second-seeded Almagro, who is coming off a victory in last week's Sao Paulo event, eliminated Stanislas Wawrinka 6-4, 3-6, 7-5 in a 2-hour, 22-minute semifinal match.
The world No. 11 improved to 10-0 on clay courts this year with the win, in which he saved a break point at 5-5 in the third set before breaking the sixth-seeded Swiss on his way to the win.
He will face fellow Spaniard Ferrer, ranked fifth in the world, after the latter posted a 6-1, 6-4 victory over Argentine David Nalbandian.
Almagro will need to overcome an 0-8 career record against Ferrer to claim the Buenos Aires crown.