World number 10 Sindhu, who had lost thrice to the Japanese in the past, including in last year's edition of Asian Badminton, avenged her losses with a 14-21 21-13 21-18 win in an hour and 13 minutes match here.
The 18-year-old will next take on Thailand's Busanan Ongbumrungpan, ranked 18th in the world, who notched up an upset 22-24 21-19 21-15 win over third seeded Korean Bae Yeon Ju in another match.
In the men's singles, Gurusaidutt, ranked 38 in the world, bounced back after the opening game loss to edge out Chinese Taipei's Wang Tzu Wei 17-21 21-13 21-19. The Indian will take on Chinese qualifier Liu Kai tomorrow.
Indian ace Parupalli Kashyap, however, went down fighting against Hsu Jen Hao of Chinese Taipei 25-23 21-17 in another hour-long match.
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In women's doubles competition, Commonwealth Games gold medallist pair of Ashwini Ponnappa and Jwala Gutta prevailed over third seeded Thailand combo of Aroonkesorn Duanganong and Voravichitchaikul Kunchala 21-11 21-18.
Guru showed a lot of grit and determination as he rallied to tire out his opponent before edging him out of contest in another one-hour match.
"The shuttles were slow so I had to really play with lots of patience," Guru told PTI after the match.
"After losing the first game, I was trailing 3-7 in the second but with the guidance of my coach (Madhumita Bist and Dwi Kristiawan) I managed to catch the shuttle up at the nets as I was going low till then.