Naomi Osaka admitted the pressure had weighed too heavily as her winning grand slam run was ended by Katerina Siniakova in the third round of the French Open.

The world number one had won 16 consecutive slam matches dating back to a third-round loss against Angelique Kerber at Wimbledon last year, taking in titles at the US Open and Australian Open and two victories here.

But she had been living extremely dangerously, and against Czech Siniakova, the world doubles number one and ranked 42 in singles, she could not find a way back, losing 6-4 6-2.

In her first two matches, Osaka had lost the opening set against Anna Karolina Schmiedlova and Victoria Azarenka before digging herself out of a hole.

This time a comeback never looked on the cards, and a tally of 38 unforced errors made for unhappy reading.

Asked how disappointed she felt, Osaka said ruefully: "It would go from one to 10 and I'm like at a 100 right now.

"Definitely I think this tournament, I have had a feeling that was different to the other grand slams. Usually I find it very freeing and fun, and this time around I was kind of tense the entire time.

"I just feel like there has been a weight on me, and I know that's because everything is sort of new. I have played the French Open before but not in this situation.

"So it hasn't been the happiest of times. Other people outside of tennis, they look at the rankings, like, 'Oh, she's supposed to win this match because the other girl is ranked five million hundred' or whatever.

"These people, they're really good but they have ups and downs. I wasn't ranked one last year. I was ranked 70. There are people that can play really good but not consistently and there are times they shine."

The pressure had not just come from outside, though, as Osaka said in Australia she was already thinking about winning all four grand slam titles this year.

"It's weird but I think me losing is probably the best thing that could have happened," she added. "I think I was overthinking this calendar slam.

"This is something that I have wanted to do forever but 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."

Siniakova next faces American Madison Keys, who battled to a 6-3 6-7 (5) 6-4 victory over Anna Blinkova.

World number one Simona Halep had dropped sets in both her opening two matches but needed only 55 minutes to breeze past Lesia Tsurenko 6-2 6-1, the Ukrainian failing to hold serve during the match.

Halep's next test will come against Polish debutant Iga Swiatek, who only turned 18 on Friday and continued her superb tournament by beating Olympic champion Monica Puig 0-6 6-3 6-3.

Swiatek won the girls' singles title at Wimbledon last summer.