Almagro, of Spain, fired nine aces in defeating the Italian 6-4, 6-4 and will meet American wild card Rhyne Williams Saturday.
Williams topped Spaniard Ruben Ramirez Hidalgo 7-6 (7-1), 1-6, 6-4 to advance to his first-ever ATP semifinals.
Fifth-seeded American John Isner reached the semis with a 6-3, 3-6, 6-3 win over Ricardas Berankis. He will take on No. 3 seed and defending champion Juan Monaco, who blitzed qualifier Robby Ginepri 6-1, 6-0.