CHARLESTON, SC, USA - No.10 seed Naomi Osaka overcame an impressive challenge from 2017 Volvo Car Open semifinalist and Porsche Tennis Grand Prix champion Laura Siegemund, 6-3, 7-6(8), to advance into the third round in Charleston.

"I guess, I'm happy most win just winning," a speechless Osaka said in her on-court interview. "I was kind of upset the whole match, to be honest, so I was just happy to be able to win today."

Siegemund enjoyed a stellar clay court season last spring and looked to be a darkhorse at the upcoming French Open before incurring a traumatic ACL injury in Nürnberg. 

As the German veteran was working her way back onto tour via the ITF Pro Circuit, Osaka was in the midst of her career breakthrough at the BNP Paribas Open, where she captured her maiden WTA title at the Indian Wells Tennis Garden.

"I'm not paying attention to everything. I'm super tired all the time and feel like everything's going by very quickly. I'm just trying to focus on my matches and think about the rest later."

In the ultimate contrast of styles, Osaka's aggression ultimately won the day over the crafty Siegemund, striking 31 winners to the German's 25, and saving a set point in the tie-break to win in just over two hours.

"I feel like my emotions were going everywhere at once," Osaka explained after the match. "And honestly, I think I only won the second set because it went to a tie-break. I feel it could have gone either way. So I feel a little bit lucky in that sense.

"I would say I was just a little bit stressed out, and I've felt like this since Indian Wells. Everything has gone by so fast, and I feel like I'm just mentally a little bit tired, so I think that's something that I need to learn how to fix."

Standing between the Japanese youngster and her first clay court quarterfinal is No.5 seed and ASB Classic champion Julia Goerges, who edged past Kristie Ahn in three grueling sets earlier in the day. 

"I've practiced with her in Wimbledon last year, and she's really good. She has a really good serve, and if she steps in, it's basically like the point's over. So I'm just really thinking of it as a challenge, and I'm just going to try to do my best and just have a really positive mindset."