Australian Open favorite Naomi Osaka heads to Melbourne seeking a fourth Grand Slam title to further fuel her ascent toward the top of the women's game on court and amplify her voice off it.

The Japanese won the last major of 2020 in New York wearing a different face mask for each match bearing the name of black Americans who had died to highlight racial injustice.

Osaka has been an outspoken supporter of the Black Lives Matter movement both in Japan and the US, where she lives, using her profile to advance the cause.

"I'm vocal because I believe in the movement and want to try to use my platform to facilitate change," Osaka told Reuters last year.

Her voice is particularly powerful not only due to her on-court success but also because of a raft of sponsors, including the recently added watchmaker Tag Heuer and business tool Workday, who are eager get behind the 23-year-old.

Osaka is now the world's highest paid female athlete, supplanting her hero and rival Serena Williams, although she believes the American is still the leading player.

"I think I'm one of the new people... As long as Serena's here, I think she's the face of women's tennis," Osaka said at a news conference on Sunday.

She has a long way to go to match Serena's 23 Grand Slam crowns ­although a second Australian Open title - Osaka triumphed in Melbourne in 2019 - would leave only the Williams' sisters having won more majors among active female players.

However, following exhibition matches in Adelaide, Osaka admitted to being a little rusty.

"I feel like there's a lot of shots that I'm missing," said the world No.3, who last played competitively at the US Open in September.