Berdych needed two tiebreakers to win in three sets over Roddick 6-7 (3-7), 7-5, 7-6 (7-3) and keep alive his hopes for a fourth career title, and his first since Halle in 2007.
Fifth-seeded Argentine Juan Martin Del Potro, fresh off an upset of top-seeded Spaniard David Ferrer in the quarterfinals, defeated fourth-seeded Richard Gasquet of France 6-3, 4-6, 7-5, and will meet Berdych in Sunday's final.
Del Potro, who turned 20 Sept. 23, is making a quick rise in the top 10 of men's world tennis. By winning the Tokyo title he can overtake James Blake at No. 8.
Gasquet failed to advance to his second straight Tokyo final. He lost to Ferrer in last year's title match.