PARIS: World number one and top seed Naomi Osaka said she was a bundle of nerves as she flirted with a first-round exit at the French Open on Tuesday before firing herself up to beat Slovakia's Anna Karolina Schmiedlova.

The 21-year-old Japanese won only nine points as she struggled to control her powerful game in a first-set horror show on her Court Philippe Chatrier debut.

But she displayed immense fighting spirit to roar back for a 0-6 7-6(4) 6-1 victory and set up a seismic second-round clash with former world number one Victoria Azarenka of Belarus.

"For me I think this is the most nervous I have ever been my entire life during a match," Osaka told reporters. "I think you could see that in the first set.

"I was literally not hitting any balls in the court. It was weird because usually the nerves go away, but it kind of stayed the entire match. Then it was a fight of willpower."

Nothing she tried came off in the opening set and it looked as though the women's draw was about to lose another big name following the exits of former world number ones Caroline Wozniacki, Angelique Kerber and Venus Williams.

But Osaka, who is the number one seed at a Grand Slam for the first time, proved she is made of sterner stuff.

"Today was a bit tough, it's one of those matches where you're not playing well, but have to find a way to win."

Mats Wilander, commentating for Eurosport, said it was reminiscent of some matches played by 23-times Grand Slam champion Serena Williams when the American has appeared out of kilter before turning things round.

FIGHTING SPIRIT

"Osaka's fighting spirit is up there with the great champions and that's what I think we're going to see from her for the rest of her career," twice French Open champion Wilander said.

"Her first set was horrendous just like Serena yesterday but somehow she turns it around and keeps going for her shots. She is similar to Serena is so many ways."

Williams also suffered a terrible first set before beating Russia's Vitalia Diatchenko 2-6 6-1 6-0 on Monday.

Osaka was all over the place at the start of the match as she appeared to struggle with the breezy conditions and the first set slipped by in 23 minutes.

Order appeared to have been restored when she went into a 3-0 lead in the second set but a brief rain delay stopped her momentum and her 90th-ranked opponent hit back.

Schmiedlova served for the match at 5-4 but Osaka hung in, only to drop serve again at 5-5.

Four times Schmiedlova got to within two points of winning the match but Osaka refused to buckle and the pressure finally began to tell as the Slovak double-faulted and then missed a backhand to take the set into a tiebreak.

Suddenly Osaka seemed to relax and after claiming the breaker she blazed through the decider to stretch her winning streak in Grand Slam matches to 15, having followed her stunning US Open win over Williams by winning the Australian Open.

She can ill-afford such a slow start in the second round, however, when she faces twice Grand Slam champion Azarenka.

"I'm expecting one of the hardest matches of the year," she said.