Boulter is seeking to end a season the place she has received two WTA titles with a flourish and has reached her first quarter-final since Eastbourne in June.
The medical victory over Okamura units up an intriguing conflict with Canadian wildcard Bianca Andreescu.
Andreescu, 24, received the 2019 US Open as a youngster however has been stricken by harm issues since.
“Bianca is an unbelievable fighter, received a Grand Slam and is taking part in some good tennis,” mentioned Boulter, who has no rating factors to defend and will transfer again into the highest 30 this week.
“It is a free swing for me on the finish of the yr and I’ve nothing to lose.”
Boulter is seeded ninth on the WTA 500 occasion within the Japanese capital, with China’s Zheng Qinwen, Russian Daria Kasatkina, Diana Shnaider and Canada’s Leylah Fernandez left within the draw as higher-ranked gamers.