World No. 1 Saina eked out a close 21-14 22-20 win over Thailand's Busanan Ongbumrungpan in the women's singles and the second seed will next take on Japan's Minatsu Mitani, an opponent against whom the Indian has a 5-2 record.
Commonwealth Games champion Parupalli Kashyap, who turned 29 yesterday, was handed a win by Japan's Takuma Ueda after he retired midway due to a back injury at 3-2 in the men's singles opening game at the Tokyo Metropolitan Gymnasium.
The duo had meet at Syed Modi International Grand Prix Gold event, where Kashyap had the last laugh.
Indonesia Masters winner H S Prannoy also notched up a thrilling 23-21 22-20 win over Wong Wing Ki Vincent of Hong Kong in 49 minutes. The World No. 12 will next square up against Korea's Lee Dong Keun.
More From This Section
However, it turned out to be a disappointing day for other Indians, including P V Sindhu and women's doubles pair of Jwala Gutta and Ashwini Ponnappa.
In men's singles, Lee Dong Keun of Korea ended B Sai Praneeth's dream of reaching any further in the tournament as he suffered a 21-23 10-21 loss.
Dutch Open winner Ajay also faltered at the first round, going down 10-21 10-21 to seventh seed Viktor Axelsen of Denmark in another men's singles match.
Glasgow Commonwealth Games silver medallists, Jwala and Ashwini played out of their skin before going down 20-22 21-18 13-21 to eighth seeds Zhao Yunlei and Zhong Qianxin of China in a 54-minute match.