Having last played in October (she retired due to injury then), Saina entered the India Open in a bid to find her feet and regain some vital match practice ahead of a big season.
Jagan also announced a cash award of Rs 7 lakh and five acres of land in Tirupati for setting up a badminton academy.
The world number 7 Indian defeated her Thai opponent, ranked three places below her, 21-14 21-18 in the pre-quarterfinal match that lasted 48 minutes.
The 26-year-old from Hyderabad will now look to cap the season with a successful defence of her maiden World championship title, which she had claimed two years ago in Basel, Switzerland.
"BWF can confirm the unfortunate news that world No.2 and men's singles defending champion Kento Momota has pulled out with injury," the game's world governing body said in a statement.