The top-seeded Ferrer needed just 70 minutes to advance with a 6-1, 6-2 rout of fellow Spaniard Albert Ramos in a quarterfinal match at Buenos Aires Lawn Tennis Club.
His next opponent will be the fourth-seeded Spaniard Almagro, who needed a tiebreaker in the first set before emerging with a 7-6 (9-7), 6-3 decision over No. 8 Jeremy Chardy.
In Saturday's other semifinal, second-seeded Fabio Fognini will take on No. 3 Tommy Robredo.
Italy's Fognini, seeking his fifth straight clay-court finals appearance dating back to last year, moved on with a 6-4, 6-3, triumph over Pablo Andujar.
Spain's Robredo, meanwhile, gained the semis in a walkover against No. 6 seed Robin Haase of the Netherlands. Robredo was ahead 6-1, 2-0 when Haase retired with a back injury.