Japan's Naomi Osaka opened her defence of the Australian Open title with a dominant win over Colombia's Camila Osorio on day one in Melbourne.

However, Osaka quickly reasserted her control and wrapped up a 6-3 6-3 win.

American Sofia Kenin, who won the title in 2020, suffered an early exit for the second year in a row as she was beaten by compatriot Madison Keys.

Former US Open finalist Keys beat 11th seed Kenin 7-6 (7-2) 7-5.

Osaka, seeded 13th, is returning to Grand Slam action after taking a four-month break at the end of last season to protect her mental health.

The four-time Grand Slam champion will play American world number 54 Madison Brengle in round two on Wednesday.

Brengle, 31, progressed after Ukrainian opponent Dayana Yastremska retired when trailing 6-1 0-6 5-0.

Osaka ready for 'unfinished business'

Osaka has spoken openly about her struggles since she won her first Grand Slam title in 2018 aged just 20.

She was criticised for opting not to speak to the media during last year's French Open, from which she ultimately withdrew and revealed her struggles with depression.

Osaka told reporters in Melbourne that she felt as though she had "a little bit of unfinished business" within tennis.

"There was a time after the French Open where I felt like everyone was judging me," said Osaka, who has won 23 of her past 24 matches in Melbourne.

"The turning point was after the US Open last year. I was just sitting in my house wondering, 'What do I want to do in the future?'

"I felt like there's still so many things that I want to do in tennis. I haven't played Wimbledon in two to three years. I want to go back and experience that whole thing."

Gauff loses on opening day

American teenager Coco Gauff, the 18th seed, was eliminated with the 17-year-old losing 6-4 6-2 to China's Wang Qiang.

The 30-year-old world number 112, who is trained by former Wimbledon champion Pat Cash, led 5-0 in the second set before sealing the victory after Gauff threatened a comeback.

Tunisian ninth seed Ons Jabeur, who injured her lower back during the Sydney Tennis Classic last week, withdrew from the tournament before her first-round match against Spain's Nuria Parrizas Diaz.

"Unfortunately, the pain is still very present and playing in such conditions could jeopardise my whole season," she posted on Twitter.

French Open champion Barbora Krejcikova made light work of Andrea Petkovic, beating the German 6-2 6-0.

Two-time champion Victoria Azarenka cruised into round two, needing only 65 minutes to beat Hungary's Panna Udvardy 6-3 6-1, while Italian 30th seed Camila Giorgi thrashed Russia's Anastasia Potapova 6-4 6-0.

Greece's Maria Sakkari, the fifth seed, beat Germany's Tatjana Maria 6-4 7-6 (7-2) and there were also wins for 22nd seed Belinda Bencic, 6-4 6-3 against Kristina Mladenovic of France, and 15th seed Elina Svitolina, who saw off another French player, Fiona Ferro, 6-1 7-6 (7-4).

Latvian 26th seed Jelena Ostapenko, who won the French Open in 2017, let a 6-2 lead in the first set tie-break slip before eventually beating Slovakia's Anna Karolina Schmiedlova 6-7 (7-9) 6-4 6-1.