Defending champion Naomi Osaka began her Australian Open campaign with a comfortable victory over young Colombian Camila Osorio.

Having taken four months off at the end of last season, Osaka returned to the match court two weeks ago and has hit the ground running in Melbourne.

The 13th seed raced into a 5-0 lead against 20-year-old Osorio, who was making her Australian Open debut, before being pegged back to 5-3.

Osaka stopped the rot, though, to take the opening set and kept her nose in front through the second to clinch a 6-3 6-3 victory.

Elsewhere, world number one Ashleigh Barty almost made the perfect start in Melbourne for a second year in a row.

Twelve months ago, Barty defeated Danka Kovinic without losing a game and she had a match point for the same scoreline against Lesia Tsurenko.

But the Ukrainian qualifier at least managed to get on the board before the top seed completed a 6-0 6-1 victory.

China's Wang Qiang, who beat Serena Williams in Melbourne two years ago, caused an upset by knocking out an error-strewn Coco Gauff 6-4 6-2 while former champion Sofia Kenin lost a high-quality encounter against fellow American Madison Keys 7-6 (2) 7-5.

Gauff, who is still only 17, said: "I think just everything disappointed me about today. I feel like in the pre-season I worked really hard and I felt like I was ready to have a good run here. Today I just didn't perform well."

Fourth seed Barbora Krejcikova raced to a 6-2 6-0 victory over Andrea Petkovic while there were also wins for Maria Sakkari, Elina Svitolina, Belinda Bencic and Victoria Azarenka.