Unseeded Chang Kai-chen of Taiwan stunned top-seeded Sam Stosur 6-4 4-6 7-6 (7-3) on Saturday to advance to the final of the Japan Open.

The 134th-ranked Chang broke Stosur, the world No.9, twice in the opening set and won 73 per cent of the points on her first serve to reach her first WTA tour final.

The 21-year-old Chang has beaten three seeded players on the way to the final where she will meet unseeded Heather Watson.

The young Briton defeated local favorite Misaki Doi 7-6 (7-2) 7-5.

Watson prevailed after breaking Doi four times in the second set to make up for losing her own serve three times.

The 20-year-old will also be appearing in her first career WTA final - just three weeks after Laura Robson became the first British woman in 22 years to reach a title match.