Osaka, Japan –  Chinese Taipei's Kai-Chen Chang knocked off top-seed Samantha Stosur in their semifinal matchup Saturday at the HP Open.

Chang smashed four aces and overcame six double faults to down the Australian Stosur, 6-4, 4-6, 7-6 (7-3) in 2 hours and 23 minutes.

Stosur, a former U.S. Open champ and last year's Osaka runner-up, was unable to secure her second trip to a WTA final this year.

The 21-year-old Chang will take on Britain's Heather Watson in the final after Watson disposed off Japan's Misaki Doi 7-6 (7-2), 7-5 in just over two hours.

Both Chang and Watson will be in search of their first-career WTA title when they meet each other for the first time on Sunday.

This week's winner will earn a first prize of $37,000.