Naomi Osaka of Japan poses for a photo with the trophy during the awarding ceremony after winning the women's singles final match against Serena Williams of the United States at the 2018 US Open tennis tournament in New York, the United States, Sept. 8, 2018. Osaka won 2-0 and claimed the title. (Xinhua/Wang Ying)

NEW YORK, Sept. 8 (Xinhua) -- Naomi Osaka from Japan stunned American Serena Williams in straight sets in the U.S. Open women's singles final here on Saturday, clinching her first-ever Grand Slam title.

The 20th seed Osaka, only 20, overpowered six-time U.S. Open singles champions and 37-year-old Serena Williams, 6-2, 6-4 in one hour and 19 minutes.