Whether she likes it or not, Naomi Osaka is a bona fide star

Naomi Osaka broke serve five times Thursday at the Australian Open to reach the third round. GREG WOOD/AFP/Getty Images

MELBOURNE, Australia -- Four months after winning her first Grand Slam title at the US Open in September, Naomi Osaka is now contending with what it means to be the player who renders others starstruck.

Osaka is now ranked No. 4 in the world and her game intimidates players like Tamara Zidansek of Slovenia, whom she beat 6-2, 6-4 on Thursday afternoon at Margaret Court Arena. When presented with the information during a postmatch news conference, Osaka, 21, looked genuinely surprised.

"No way," she responded.

"I feel old," Osaka said when asked what it's like to be a person other tennis players consider a star. "Wow, that's kind of crazy. I don't know. Hey, what did she say though? When you play someone, like for me, when I play, like Venus or something, I'm starstruck, too. It's a bit weird when you tell me there's someone I'm playing that feels that way."

It was Zidansek's first time playing in the second round of a Grand Slam.

"I'm happy with how I managed to play today," Zidansek said in her postmatch news conference. "I was really trying, just staying with her. ... Her serve is really good. She puts pressure, she loves to attack, and she's really good at that, so you have to be very consistent to try to be at her level."

Through two rounds at the Australian Open, Osaka has appeared poised, sure of herself, and fairly unflappable. It's a marked change from September, even before she reached the final of the US Open, where she beat Serena Williams in a match fraught with penalties and controversy.

It was a bruising way to inject herself into the upper echelon of women's tennis, but it has been useful, too. Osaka was famously introduced to new fans and casual watchers of tennis with a towel over her head and tears streaming down her cheeks, apologizing for defeating Williams. She seems to have gained years of maturity in a matter of months.

"What makes me relaxed is the fact that I know I've put in a lot of time during the offseason on my fitness," Osaka said. "I feel like I can sort of relax and let the other person do whatever they want, and I have confidence that I can run it down."

Saturday, Osaka will face No. 28 Su-Wei Hsieh of Taipei, who has established a reputation for frustrating opponents with a style some have described as "crazy."

"I feel like you already walk into the match knowing she's going to be doing a lot of tricky stuff," Osaka said of Hsieh. "It's not anything new. I think that's the mentality I have to have."