19-year-old Saina came back strongly after losing the opening game to overcome 10th seed Petya Nedelcheva of Bulgaria 18-21, 21-18, 21-10 in a 57-minute encounter.
Saina said, "In the second game, it was really tough as I was leading 18-11 but she bounced back but I think I kept my cool and it paid off."
Sixth-seeded Nehwal will now clash with second-seeded Chinese Wang Lin, a 21-10, 23-21 winner over Korean Hwang Hye Youn.
Saina also said, "The third game was really well but I am not happy with the first game as I made too many mistakes. I was involving in more long rallies as my dribbles were not well and she was smashing the shuttle well but my defense was good."
When asked if she felt fatigued, Saina said, "I was not feeling tired and I think that is a good sign especially when I am playing a tougher opponent in the next round."
"It will be a very tough match against Wang but I will give my 100 per cent, Saina added.