Date Krumm, who is one day short of her 40th birthday, broke the 23-year-old Russian to go up 5-3 in the third set and won the final game when Sharapova's backhand went wide.
"To play against a former World No. 1 and defending champion, I knew I had to play to the best of my ability," said Date Krumm, who returned to competitive tennis in 2008 after a 12-year layoff.
Story continues below ↓advertisement | your ad hereSharapova, who is the tournament's 12th seeded player, had 11 double faults in the match that lasted 2 hours and 9 minutes at Ariake Colosseum.
Sharapova broke Date to go up 3-2 in the final set and was leading 40-love in the sixth game when she double faulted twice before being broken by Date Krumm.
"Momentum is so big in tennis," Sharapova said. "If you give your opponent a chance they can get confident and take the momentum away."
It was the first meeting between the two players. Sharapova said she was impressed with Date Krumm's ability and fitness after such a long layoff.
"It's incredible," Sharapova said. "It just shows you how she has stayed in such great shape while away from the game. She is incredibly fit."
Date Krumm had just returned from Seoul where she lost in the quarterfinals of the Korea Open on Friday. She said the quick turnaround was not easy.
"I just came back from Korea yesterday and was really tired," she said. "My body felt a little better today but this surface was a lot faster that the one in Korea."
In second-round matches, third-seeded Jelena Jankovic of Serbia defeated Alona Bondarenko of Ukraine 6-4, 6-1, and sixth-seeded Agnieszka Radwanska of Poland coasted to a 6-2, 6-3 win over Olga Govortsova of Belarus.
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