Naomi Osaka's bid for a third tour title ended in a straight-sets semifinal defeat to Anastasija Sevastova at the China Open on Saturday.

The Latvian, ranked 20th in the world, knocked off the U.S. Open champ 6-4, 6-4 in 1 hour, 31 minutes. According to the WTA website, the victory over the sixth-ranked Osaka was Sevastova's fourth over a top-10 opponent this season.

"You have to stay aggressive, you have to stay concentrated," Sevastova said afterward in an on-court interview. "Naomi, she's a great player, one of the best this year."

"She's so confident. So you have to stay there. You have to return every ball, and play good on your service game."

The 20-year-old Osaka, whose mother is Japanese and father Haitian, hit 24 winners but also made 42 unforced errors and managed to convert just one of her four break opportunities.