Kim Birrell has missed out on lifting her maiden WTA title in the Japan Open in an anti-climactic finale to what had proved a huge breakthrough week for the Australian hopeful.

On a busy Sunday at the hardcourt event in Osaka, the former Aussie No.1 Birrell, who's slipped back in the rankings to 150, had to play two matches in the space of a few hours after the previous day's play had been wiped out by rain.

It all started well as the 26-year-old Queenslander won her sixth straight match, including two qualifiers, in her first ever WTA semi to beat home favourite Aoi Ito 6-3 6-4 and power into her maiden tour championship match.

In both sets, she recovered an early deficit to race home to victory in 75 minutes, putting her in line to emulate fellow Queenslander Sam Stosur, a winner of the 2009, 2013 and 2014 titles in Osaka and to become the first qualifier to win the tournament since Zarina Diyas in 2017.

But when she returned to the court just over an hour later, it was another qualifier, Dutchwoman Suzan Lamens, the world No.125, who proved much the stronger, winning comfortably 6-0 6-4 in 73 minutes.

There was a brief moment of hope in the second set when the Gold Coast player broke for a 3-2 lead but Lamens broke back to love and then cracked Birrell's serve for a sixth time before easing to the title.

It was a disappointing end to a big week for Birrell, but her substantial consolation will be to rise 39 places to world No.111, closing in on her career-best ranking of 100.

In another WTA final in China on Sunday, Daria Kasatkina defeated teenage Russian compatriot Mirra Andreeva 6-0 4-6 6-4 to win the Ningbo Open for her second title of the year.

While Kasatkina will return to the top 10 with her triumph as the new world No.9, 17-year-old Andreeva was left in tears at missing her own chance for a second title of the year.