PARIS -- This was one deficit too big to overcome for Naomi Osaka, whose Grand Slam winning streak is over.

The No. 1-ranked Osaka couldn't muster a comeback after falling way behind yet again at the French Open, losing 6-4, 6-2 in the third round to No. 42 Katerina Siniakova of the Czech Republic on Saturday.

"I just feel like there has been a weight on me, kind of," said Osaka, who was seeded No. 1 at a major tournament for the first time.

She had won her past 16 matches at majors, allowing her to lift the trophies at the US Open last September and Australian Open in January. That run also included two victories at Roland Garros after trailing by a set and a break each time.

"I could see," Siniakova said, "that she's not so confident like she was."

But Osaka said Saturday that she felt tired and was dealing with a headache.

Her mounting mistakes just kept accumulating against Siniakova, who had never reached the fourth round in singles in 18 previous Slam appearances. She is better known for her doubles success, winning championships at the French Open and Wimbledon last year and topping the rankings.

She is the first woman ranked No. 1 in doubles to defeat the singles No. 1 in more than 30 years, according to the WTA: The last occasion was when Martina Navratilova beat Steffi Graf at the 1987 US Open.

"I mean, it's incredible. It's amazing. It's the thing I couldn't believe," said Siniakova, who will face 2017 US Open runner-up Madison Keys next. "It was my best tennis."

It decidedly was not Osaka's, who quickly gathered her things and headed to the Court Suzanne Lenglen locker room when the lopsided match was finished.

She wound up with a hard-to-believe 38 unforced errors; Siniakova made only 13.

And Osaka, so good lately at the biggest moments on her sport's biggest stages, wasn't able to come up with the goods on the hottest day of the tournament so far, with the temperature topping 80 degrees (approaching 30 Celsius).

One key statistic: Osaka compiled seven break points in the first set but failed to convert a single one. She was 0 for 4 on break chances when Siniakova served out that set, then never managed to earn one in the second.

Clay has never been Osaka's best surface. Her power game is served better by the speed of hard courts, in particular. That's why she still has not made it to the round of 16 at the French Open.

The first tennis player from Japan to be ranked No. 1 thought she was better suited to contend this time and spoke about eyeing a third consecutive major title -- and moving halfway to a true Grand Slam.

"It's weird, but I think me losing is probably the best thing that could have happened. I think I was overthinking this calendar Slam. For me, this is something that I have wanted to do forever," Osaka said. "But I think I have to think about it like: If it was that easy, everyone would have done it. I just have to keep training hard and put myself in a position again to do it, hopefully."

After going just 9-11 on clay over her career until this season, she was 9-1 in 2019 until Saturday's setback.

Osaka's exit, a day after No. 2 Karolina Pliskova lost, leaves defending champion Simona Halep, at No. 3, as the highest-seeded woman remaining. Halep needed only 55 minutes to get to the fourth round with a 6-2, 6-1 victory over No. 27 Lesia Tsurenko.

Keys, a semifinalist in Paris a year ago, advanced by beating qualifier Anna Blinkova 6-3, 6-7 (5), 6-4.

Information from The Associated Press was used in this report.