Image caption, Katie Boulter's last WTA title came at the Ostrava Open in February Published 5 minutes ago Katie Boulter has lost in the Japan Open semi-finals, in her first match since reclaiming the British number one spot from Sonny Kartal.
Kartal moved above Boulter in the world rankings by reaching the final of last week's Wuhan Open.
But Boulter's run to the last four in Osaka, which included a victory over Antonia Ruzic in the quarter-finals, will be enough for her to go back above Kartal when the rankings are next updated.
However, the 30-year-old missed the chance to reach the final, and a shot at a fifth WTA singles title, losing 6-1 6-4 to doubles world number one Siniakova.
Eighth seed Boulter rallied after being swept aside in the opening set, going a break up at the start of the second.
But Siniakova, also 30, maintained her bid for a first singles title in four years by claiming two hard-fought breaks of her own to wrap up victory in 85 minutes.
She will now play 2023 champion Ashlyn Krueger in Sunday's final after the 22-year-old American beat compatriot and top seed Ann Li 6-4 6-7 (4-7) 6-3.
