After taking the first set in 30 minutes behind a blistering forehand, the second-seeded Russian quickly went up 3-0 in the second set before faltering.
Thailand's Tamarine Tanasugarn suddenly came to life, breaking Sharapova in the fourth game and winning five of the next seven to make it 5-5.
Sharapova dug deep in the 11th game, however, breaking again and then closing out the match with an ace to finish the contest in 1 hour, 31 minutes at a covered Ariake Colosseum.
The annual WTA Tour tournament is normally an outdoor event, but rain in the late morning forced the closure of the roof over the main court and suspension of play on the outdoor courts.
In other second-round action, seventh-seeded Marion Bartoli of France defeated Ayumi Morita of Japan 6-3, 0-6, 6-3.
Bartoli prevailed in a baseline battle in 2 hours, 18 minutes despite a second-set whitewash. She overpowered Morita with a strong backhand in a final set that saw breaks of serve in the first three games.
Morita committed several unforced errors in the third set. Serving to stay in the match, Morita staved off four match points before finally succumbing.
Also, qualifier Mandy Minella of Luxembourg rallied to beat Japanese veteran Kimiko Date-Krumm 1-6, 6-3, 6-3, and 12th seed Ana Ivanovic of Serbia beat qualifier Anastasia Rodionova of Australia 6-4, 6-0.
Jelena Jankovic of Serbia will take on Victoria Azarenka of Belarus later Monday.
Defending champion Caroline Wozniacki of Denmark, the top-seeded player in the $2,000,000 tournament, has a first-round bye and will meet the winner of the match between Rebecca Marino of Canada and Jarmila Gajdosova of Australia on Tuesday.
US Open champion Samantha Stosur of Australia also has a first-round bye. She will take on the winner of the match pitting Maria Kirilenko of Russia against Erika Sema of Japan on Tuesday.