The 40-year-old saw off Daniela Hantuchova 7-5, 7-5 in just under two hours at the season-ending event, a victory that should see her move to around 46th in the world rankings.
Date Krumm, who in August became the oldest player in more than quarter of a century to rank in the top 50, needed four set points to secure the 66-minute opener against her Slovak opponent, who has won three career titles from 10 finals.
The Japanese player was broken to love while serving for the match at 5-4 in the second set, but broke back a game later and held on to end her week on the Indonesian resort island with a win.
The final of the event -- for winners of WTA International tournaments during 2010 -- will be decided later on Sunday when 2008 French Open champion Ana Ivanovic of Serbia takes on Russian Alisa Kleybanova.
Date Krumm, a fan favourite in Asia who was once ranked fourth in the world, quit the tour in the 1990s but has made a successful comeback over the past three seasons.