India's Saina Nehwal entered the quarterfinals of the women's singles after posting a hard-fought victory over Eriko Hirose of Japan in the Singapore Badminton Super Series on Thursday.The world number two Indian took a little more than an hour to pack off the Japanese 16-21 21-16 21-9 at the Singapore Indoor Stadium.The 23-year-old from Hyderabad will next take on Lindaweni Fanetri of Indonesia in the last-eight stage.