The 18-year-old broke her opponent in the opening game of the match and never looked back as she comfortably progressed 6-3 6-1 to set up a last four clash with 2011 US Open champion Samantha Stosur.
"I think I just played a pretty solid match overall," Keys told the official WTA website.
"It was definitely windy and I wasn't able to hit as many big serves as I was yesterday as I was trying to play the percentages a bit more. The conditions are just something you have to learn to deal with, I just tried to keep moving my feet and judge when to go for it."
Stosur survived a second set blip to win 6-1 3-6 6-3 against home favourite Misaki Doi.
"I know her a little bit - we played in Indian Wells this year - she's tall, very strong, has a very big serve and hits the ball hard," said Stosur.
The other semifinal sees Canada’s Eugenie Bouchard face Kurami Nara after the pair came through three set matches against Barbora Zahlavova Strycova and Polona Hercog respectively.