Nishikori, the third seed at the ATP 250 event, edged past Stan Wawrinka 7-6 (7-3) 6-3 in their semi-final.
The Japanese star was clinical, converting both of his break points as Wawrinka won just one of five.
Nishikori booked his spot in a 21st ATP World Tour final after one hour, 41 minutes against the Swiss second seed.
Awaiting him in the decider is Dimitrov, who continued his bright start to the year with a 7-6 (9-7) 6-2 victory over top seed Milos Raonic.
Raonic, the defending champion and finalist the past two years, won just 13 points against the Dimitrov serve.
The Bulgarian seventh seed, runner-up in 2013, battled through a first-set tie-break before breaking serve twice in the second set.
Sunday's final will be the 10th of his career as he targets a fifth ATP World Tour title.
Nishikori holds a 3-0 win-loss record against Dimitrov, but was pushed to three sets when they met last year.