The last time the two met was at last year's Rio Olympic Games where the diminutive Japanese came out on top against Ratchanok, who won a treble of Junior World Championship titles. However, the fifth-ranked Thai managed to extract revenge on Yamkuchi this time even if she had to work hard in the opening set.
Standing between Ratchanok and her maiden All England title in Sunday's showdown is the world number one Tai Tzu Ying of Taiwan who sneaked past third-ranked South Korean Sung Ji Hyun after the three-set battle.