Naomi Osaka survived a major scare to beat Anna Karolina Schmiedlova and continue her winning grand slam run in the opening round of the French Open.

The 21-year-old from Japan won both the US Open and Australian Open titles to climb to the top of the world rankings and had spoken of her desire to claim all four this year.

That looked a long way away when she lost the opening set to love in just 20 minutes, and Schmiedlova twice served for the match in the second set, but Osaka dug in to win 0-6 7-6 (4) 6-1.

She is likely to have to raise her level significantly if she wants to progress any further with former world number one Victoria Azarenka her next opponent.

Had she lost, Osaka would have become just the second women's top seed to lose in the opening round at Roland Garros after Angelique Kerber two years ago.

Like Kerber, Osaka is not at her best on clay but she had had a reasonably encouraging build-up and it had certainly not been expected that Schmiedlova would cause her too many problems.

The 24-year-old Slovakian, who is ranked 90th, had lost her last nine first-round matches at the grand slams dating back to the 2015 US Open.

But Osaka looked unsettled from the start in cool and windy conditions and Schmiedlova took full advantage.

The world number one looked to be getting a foothold in the match when she won the first three games of the second set but a brief interruption for rain disrupted her again and Schmiedlova levelled at 3-3.

Osaka buried her head in a towel after dropping serve again at 4-4 to leave her opponent serving for the match.

Osaka composed herself to break back only to drop serve again, and Schmiedlova came close to taking it the second time, coming within two points of victory.

But she could not get over the line and, after winning the tie-break, Osaka ran away with the third set.