PARIS — Naomi Osaka's quest for a third consecutive Grand Slam title almost came to an abrupt end on Tuesday as a number of top players struggled to book their spots in the second round of the French Open.

On a windy and chilly day at Roland Garros, world number one Osaka, who won the U.S. and the Australian Opens, lost the opening set to love against Slovakian Anna Karolina Schmiedlova before rallying back for a 0-6 7-6(4) 6-1 victory.

Defending champion Simona Halep, Osaka's potential semi-final opponent, lost her way in the second set against Australian Ajla Tomljanovic in a 6-2 3-6 6-1 victory on a windswept Court Philippe Chatrier.

In the men's draw, German fifth seed Alexander Zverev was also pegged back during his match against Australian John Millman and needed five sets to progress after winning the first two.

Last year's semi-finalist Juan Martin Del Potro also huffed and puffed into round two with a four-set win against Nicolas Jarry of Chile.

Victoria Azarenka avoided the fate of fellow former world number ones Angelique Kerber and Caroline Wozniacki, who were knocked out in the first round, when she beat 2017 champion Jelena Ostapenko in straight sets.