Boulter is ranked 33rd in the world after a year which has yielded two WTA titles and a breakthrough into the top 30.
While she has been unable to go past the third round of a major, Boulter has regularly asserted her authority with her powerful baseline game.
That is what happened in Tokyo as the gulf between Boulter and Okamura showed.
Providing greater consistency from the baseline, and showing glimpses of craft, Boulter’s level was too much for Okamura to handle.
“I’m playing some good tennis,” said Boulter, who reached her first quarter-final since Eastbourne in June.
The clinical victory sets up an intriguing clash with Canadian wildcard Bianca Andreescu.
Andreescu, 24, won the 2019 US Open as a teenager but has been plagued by injury problems since.
“It’s a free swing for me at the end of the year and I have nothing to lose,” said Boulter, who has no ranking points to defend and could move back into the top 30 this week.
