Almagro, of Spain, breezed to a 6-1, 6-3 win over Frenchman Gilles Simon in just 68 minutes.
Baker took down Nikolay Davydenko 6-7 (5-7), 6-4, 6-2. He broke the Russian's serve eight times.
Almagro and Baker meet Saturday for the title.
The Spaniard is 11-5 in finals in his pro career.
Baker, 27, once considered a future star in men's tennis, has battled back from injuries and surgeries. He is now in his first ATP final.
The event is a tuneup for the French Open, which begins Sunday.
Swim Week Miami Beach 2014 [PHOTOS]