The 25-year-old will rise to fourth in the world as a result of his final showing in Mexico, but should he win the event and Rafael Nadal fail to triumph in Argentina then Nishikori will take up third position in the ATP rankings.
The top seeded Nishikori was made to work for his victory over Anderson, coming back from a break down in the final set to beat the South African in just over two hours.
Nishikori broke the big-serving Anderson twice in the first set to take the opener 6-2, but Anderson bounced back to take the second 6-3 after claiming the lone break of serve.
It was the world number 15 who took the early initiative in the decider, but Nishikori was not to be denied, breaking Anderson twice to take the final set 6-3.
In Saturday's final, Nishikori will take on David Ferrer, who beat unheralded American qualifier Ryan Harrison in three sets.
The 22-year-old Harrison shocked the Spaniard in a lengthy first set but then showed why he has never reached an ATP Tour final when he dropped the next 12 games to go down 4-6, 6-0, 6-0.
Nishikori has won seven of his 10 career meetings with Ferrer, the latest being a straight sets win in the fourth round at the Australian Open last month.
Ferrer is a three-time winner in Acapulco, having won the title back to back from 2010 to 2012.