Naomi Osaka has launched her Australian Open title defence with a gritty first-round win over rising young Czech Marie Bouzkova.

The Japanese third seed was made to fight back from a service break down in the second set before advancing with a 6-2 6-4 victory over Bouzkova in Monday’s opening match on Rod Laver Arena.

Third-seeded Osaka will play Zheng Saisai in the next round after the Chinese beat Russian qualifier Anna Kalinskaya 6-3 6-2.