Seventh seed Saina, who improved a rung in the world rankings today to be sixth, lost 17-21 21-9 15-21 to Porntip, who jumped three places to world number 10, at the Hong Kong Coliseum here.
Ajay Jayaram's campaign in the men's singles competition also came to an end after he went down 18-21 12-21 to Sony Dwi Kuncoro of Indonesia in a 36-minute match.
Saina tried to dominate the nets but Porntip didn't give her too many opportunities. She had all the answers to Saina's smashes, four more than the Indian.
The first game saw Porntip breaking free at 10-10 after Saina had opened up a 7-4 early lead. The Thai girl was better prepared for the battle as she registered five straight points to create a huge gap between her and Saina and then kept her nose ahead to lead 1-0.