PARIS, France - Top seed Naomi Osaka overcame a slow start to meet a tough challenge from Anna Karolina Schmiedlova, outlasting the former World No.26, 0-6, 7-6(4), 6-1 at Roland Garros on Tuesday.

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"I think this is the most nervous I have ever been my entire life during a match," she admitted after the match. "I think you could see that in the first set. I was literally not hitting any balls in the court.

"For me, today was weird because usually the nerves go away, but it kind of stayed the entire match. Then I just felt like it was a fight of willpower. I managed to win in the end."

Two points from defeat, Osaka improved her Grand Slam match winning streak to 15 straight and kept her hopes of a third straight major title alive after one hour and 54 minutes on Court Philippe-Chatrier.

"I can give you logical reasons, but I'm not really a logical person," she joked when asked to explain her nerves. "So it might be something else.

"It was my first time playing a Grand Slam as No.1. I won the last two [majors], so I kind of want to win this one really bad. I have never played on Chatrier before. This was my first time.

"I kind of feel like I'm having the thought of wanting to prove myself again."

Schmiedlova has endured a topsy-turvy career her breakthrough 2015 season - when she won two titles - and nearly fell outside the Top 300 two years ago. Back in the Top 100 and playing a World No.1 for the first time, the Slovak showed few nerves against the reigning US Open and Australian Open champion.

Osaka, by contrast, has dealt with physical struggles despite solid results throughout the clay court season, withdrawing from both the Porsche Tennis Grand Prix semifinals and the Internazionali BNL d'Italia quarterfinals with an abdominal and hand injury, respectively. 

"Today was completely fine. I didn't feel anything. Probably looked like I felt something, but, no, it was fine today."

Second up on the new Chatrier stadium on Day 3, Osaka's laser-like groundstrokes lacked their typical range in the first set, resulting in 13 unforeced errors as Schmiedlova, who began 2019 with a runner-up finish at the Hobart International, rolled through without losing a game.

The Slovak won her third career title last spring on clay at the Claro Open Colsanitas, but soon found herself on the opposite end of a 3-0 lead to start the second set. She clawed her way back on serve only for a brief rain delay sent both players off court.

Osaka dug deep to break Schmiedlova as she served for the match, but dropped serve once more - flashing a sarcastic thumbs up to her coaching team - as the unseeded 26-year-old earned a second chance to secure the upset.

"I was just thinking, like, 'I have so many shots that I normally feel like I would hit well, and then it was just one of those,' It was definitely sarcastic. I was kind of thinking, 'Do you guys see this amazing tennis I'm playing right here? Thumbs up.'

"It's one of those matches where you're not playing well but you have to find a way to win. For me, I've just begun learning how to do that."

Closing in on victory, she missed a pair of backhands and Osaka leveled the set once more, forcing a tie-break on her fourth break point of what became a marathon 12th game.

"I think everybody saw that I was really close," Schmiedlova said after the match. "And it did hurt that I lose today because I had so many chances.

"She's No.1 in the world and amazing player. I admire her so much. I think I could have won today, but maybe next time."

The Japanese star grabbed the first mini-break of the Sudden Death, and took another following the change of ends. Down four set points, Schmiedlova saved the first with a searing backhand return but Osaka ultimately prevailed, taking the tie-break behind a big forehand that forced the Slovak into a miss.

Showing her signature mix of aggression and athleticism, Osaka nabbed the first break of the deciding set, turning defense to offense and smacking a ruthless backhand to take the early initiative.

"I think it's really important for tennis players to learn, especially since we have so many opportunities to do that," Osaka said. "We have games and we have sets and we even have points if you're really good.

"I definitely think it's one of my strengths, but at the same time, I think it might be a bit of a weakness or a liability, because I overthink most of the time. There is always a problem, but then you think that you have multiple solutions instead of just one."

The World No.1 only grew in confidence from there, moving into a 5-1 lead with another forehand stunner - finishing with a total of 32 winners to just 25 unforced errors in the final two sets.

Racing out to a 0-40 lead in the final game, Osaka converted her first match point to seal her place in the second round.

Things won't get easier for the top seed, however, as she'll next face former World No.1 Victoria Azarenka, who overcame 2017 French Open champion Jelena Ostapenko earlier in the day The two have played twice before, with Azarenka winning their 2016 Australian Open clash while Osaka avenged the lost last year in Rome.

"She's been playing really well recently, and there is no way that it's going to be a similar match to the one I played her in Rome last year. So I'm expecting, like, one of the hardest matches of the year."