Naomi Osaka lost in straight sets at the Birmingham Classic grass-court tournament on Thursday — and could soon lose her No. 1 ranking, too.

The two-time Grand Slam champion from Japan never looked comfortable in a 6-2, 6-3 loss to Yulia Putintseva in the second round, choosing to sit on the court instead of her chair at changes of ends.

Osaka would have guaranteed holding onto top spot in the rankings heading into Wimbledon, which starts July 1, by reaching the final in Birmingham but she could now be ousted by No. 2 Ashleigh Barty.

The newly crowned French Open champion beat Jennifer Brady 6-3, 6-1 in a match interrupted by rain to advance to the quarterfinals.

Barty has made a strong transition from clay to grass as she seeks a title win that would lift her to No. 1 status.

"The stars have aligned a little bit for me and I think when you get those opportunities, you have to do your best to take them with both hands," Barty said.

"That's what we have been able to do over the last month in particular but I feel like I'm comfortable in my own skin. I feel like I know exactly how I want to play in most matches, and it's just about going out there trying to execute as best I can."

Osaka, meanwhile, has slumped to a second straight early exit from a tournament, after losing in the third round of the French Open to unseeded Katerina Siniakova from the Czech Republic.

Venus Williams, a five-time Wimbledon champion, joined Barty in the quarterfinals with a 6-3, 6-2 win over Wang Qiang.