Stosur falls in first round at Japan Open

Samantha Stosur has made an unsuccessful return in her first WTA tennis match since the French Open in early June.

Samantha Stosur is Australia's third highest ranked women's tennis player. (AAP)

Samantha Stosur has suffered a three-set defeat in her long-awaited comeback from injury at the Japan Open on Wednesday.

Australia's 2011 US Open champion went down 3-6 7-5 6-1 to Spaniard Sara Sorribes Tormo in the first round of the Japan Open in Tokyo.

Stosur, the fifth seed in Tokyo, hasn't played since suffering a stress fracture in her right hand during a fourth-round loss to eventual Roland Garros champion Jelena Ostapenko.

Jana Fett advanced to the second round by beating top-seeded Kristina Mladenovic 6-4 6-3.

Frenchwoman Mladenovic rallied briefly by winning three games in the second set before the 20-year-old qualifier from Croatia served out the victory.

Defending champion Christina McHale of the United States, second-seeded Zhang Shuai of China, local hope Kurumi Nara and Zarina Diyas also advanced to round two.

In second-round action, Belgian third seed Elise Mertens defeated Magda Linette 6-1 7-5, Japan's Miyu Kato upset fourth-seeded Czech Kristyna Pliskova 7-5 6-3 and Aleksandra Krunic of Serbia was too good for American seventh seed Alison Riske 6-3 6-4.