Blake beat Spadea for only the second time in eight tries, 7-6 (7-2), 6-4.
Blake will next meet Hyung-Taik Lee, who surprised third-seeded Marat Safin, 4-6, 7-5, 6-4. Lee came back from a break down in the third set.
Nicolas Kiefer also advanced with a 7-6 (7-5), 6-1, win over Michael Berrer. Kiefer's semifinal opponent will be Radek Stepanek, who was a 6-4, 6-2, victor over Zack Fleishman.