
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.
Tanasugarn suddenly came to life, breaking Sharapova in the fourth game, and winning five of the next seven games 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.
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.
Qualifier Mandy Minella of Luxembourg rallied to beat Japanese veteran Kimiko Date-Krumm 1-6 6-3 6-3.
In early action, 12th seed Ana Ivanovic of Serbia beat qualifier Anastasia Rodionova of Australia 6-4 6-0.
Defending champion Caroline Wozniacki of Denmark, the top-seeded player in the $2-million tournament, will meet the winner of the match between Rebecca Marino of Canada and Jarmila Gajdosova of Australia today.