Almagro, who captured last week's ATP Tour stop in Sao Paulo, defeated qualifier Igor Andreev 6-3, 7-5 in the clay-court event. The win in Brazil boosted Almagro to No. 11 in the world rankings, and he is seeded second in this tournament behind Spanish countryman David Ferrer.
Stanislas Wawrinka will meet Almagro in the semifinals after defeating No. 4 seed Kei Nishikori 6-4, 6-2.
Ferrer also reached the semifinals with a 6-2, 6-4 decision over Fernando Gonzalez. David Nalbandian, who won this tournament four years ago, will take on Ferrer after breezing by Carlos Berlocq 6-0, 6-3.