Ratchanok was nowhere near her best as a flurry of errors flowed from her racquet to hand South Korean world No 10 Sung Ji Hyun a 21-12 21-12 victory.
Her coach Patapol Ngernsrisuk said the Thai No 1 is having a back injury which has bothered her since the Malaysia Open last week. But he insisted the
injury was not serious.
Four-time champion Lee Chong Wei eliminated last Thai Kantaphon from the tournament with a 21-13 22-20 win in the men’s singles.
The two, along with the other national players, will hope to redeem their pride in the Thailand Open Super 500, which starts on Tuesday at the Nimibutr National Stadium.