No. 6 seed Nishikori of Japan followed up Friday's upset of top-seeded American Mardy Fish with a 6-3, 7-5 defeat of 11th-seeded Pablo Cuevas of Uruguay, moving on to the championship match.
American Sweeting, meanwhile, prevailed over former Clay Courts champion Ivo Karlovic of Croatia, 7-6 (7-3), 6-3.
Nishikori gained his second career final. He notched a win at Delray Beach in 2008 in his other title match.
Sweeting, who has reached his first career final, fell to Nishikori at Delray Beach this year in the pair's only previous meeting.
Swim Week Miami Beach 2014 [PHOTOS]