World number seven Saina thrashed Iran's Soraya Aghaeihajiagha (2-0) 21-7 21-6 in a women's singles round of 16 match at the Gyeyang Gymnasium.
The top Indian shuttler needed just 18 minutes to seal the match in her favour. While Saina took 18 minutes to win the first game, she pocketed the second in just four minutes against her hapless opponent.
Seeded sixth, Saina would be would up against no. 2 seed Wang Yihan of China.
Sindhu won the first game 22-20 in 19 minutes but went down 16-21 20-22 in the next two games, to bring an end to her campaign. Up against a higher-ranked opponent, Bellaetrix always seemed ready for the challenge in the 62-minute match.
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Earlier, Parupalli Kashyap made the men's singles pre-quarterfinals by registering a straight-game win over Afghanistan's Iqbal Ahmad Shekib.
Glasgow Commonwealth Games gold medallist Kashyap, having received a bye in the opening round, defeated his Afghani opponent 21-6 21-6 in just 17 minutes to book a place in the next round at the Gyeyang Gymnasium.
The story remained same in the second game as well with the 28-year-old Indian taking just a minute longer than the first to see off Shekib.
In a mixed doubles round of 32 match however, India suffered a reverse with Akshay Dewalkar and Pradnya Gadre losing 20-22 21-17 13-21 to Triyachart Chayut and Yao Lei of Singapore. They lost the match in 42 minutes.
But Manu Attri and N Sikki Reddy won their mixed doubles round of 32 match against Rasheed Aishath Afnaan and Sharafuddeen Nasheeu 2-0 (21-8 21-4) in just 15 minutes.