The World No. 6 took 39 minutes to win the contest at the Musashino Forest Sport Plaza in Tokyo that earned a spot in the last eight.
The victory gave Ratchanok, nicknamed May, eight consecutive wins over the World No. 23.
She will meet World No. 1 Tai Tzu Ying of Taiwan in the next round.
World No.13 Busanan “Cream” Ongbamrungphan ended her quest for a medal today, losing 15-21, 15-21 to No.8 An Se-Young of South Korea.
The Thai fought for 53 minutes but she could not break the stiff defence and decisiveness of the South Korean. Busanan has failed to take a set in their three encounters.
Her exit left Ratchanok as the only Thai player still in the contest.