Doi, at 22 about half of Date-Krumm's age, emerged a 7-6 (7-3), 6-4 winner over Date-Krumm. She lost both of Date-Krumm's break opportunities in the first set and didn't see a break point in the second.
Date-Krumm has won the Japan Open four times, including in 1992, three weeks before Doi's first birthday. Date-Krumm won the event from 1992-96. She was runner-up in 1995.
Sixth-seeded Madison Keys blasted past Zhang Shuai 6-4, 6-0 by winning all but three -- 24-of-27 -- of the points in the second set. Keys fought off three break points in the first set but dropped just one point on serve in the second.
Zheng Jie defeated ninth-seeded Kristina Mladenovic 6-7 (5-7), 6-2, 6-0. She won about two-thirds of the points over the last two sets.
Keys goes against Zhang and third-seeded Samantha Stosur draws Doi in Friday's quarterfinals in the top half of the draw. Hercog is to play Kurumi Nara and fifth-seeded Eugenie Bouchard is to meet Barbora Zahlavova Strycova in the other quarterfinals.