World number one Naomi Osaka avoided a premature end to her bid for a third straight Grand Slam title by coming from behind to reach the French Open second round.

Osaka, 21, twice had to stop Slovakia's Anna Karolina Schmiedlova serving out the match before winning 0-6 7-6 (7-4) 6-1 at Roland Garros in Paris.

Schmiedlova, ranked 90th in the world, made very few errors until victory was in sight, but the pressure of a career-best win told as Japan's Osaka fought back.

The US Open and Australian Open champion, playing in her first Grand Slam as the top seed, will face two-time Grand Slam champion Victoria Azarenka of Belarus in the second round.

Azarenka, 29, beat 2017 French Open champion Jelena Ostapenko 6-4 7-6 (7-4) in one of the most anticipated ties of the round.

Coming into Tuesday's opening match, Osaka had lost only once in the first round of a Grand Slam - at Roland Garros against Alison van Uytvanck in 2017.

That tally looked set to double after a dismal 22-minute first set in which Osaka won nine points.

Osaka, who has been struggling with a hand injury recently, never looked comfortable in the first half of the match, making 34 unforced errors in the opening two sets.

Schmiedlova, the 24-year-old playing her first match against Osaka and with a solitary win against a top-10 player, made only five unforced errors on her way to going a set and a break up.

But, tightening up as victory loomed, allowed Osaka to break back at 5-4 and 6-5.

From that point Schmiedlova never looked like threatening again.

Osaka's body language steadily improved, along with her ball striking, and she dropped only six more points to take the final five games.

While she did enough to advance, she will know she must improve with Azarenka - and potentially Serena Williams further down the line - looming.