ROGER FEDERER prefers to think of Rafael Nadal or Novak Djokovic as the favourites for the Australian Open title, which begins to, despite entering as defending champion and having a worry-free preparation.

"I play down my chances just because I don't think a 36-year-old should be a favourite of a tournament," Federer said today on the eve of the year's first grand slam tournament. "It should not be the case.

"That's why I see things more relaxed, you know, at a later stage of my career."

The 19-time major winner can afford to relax slightly longer, given the half of the draw that he shares with Djokovic doesn't start until day two. Top-ranked Nadal will get under way tonight against Victor Estrella Burgos in the Rod Laver Arena, where he lost the final in five sets to Federer last year.

All four singles finalists were 30 or older here last year in what became a tournament for the ages and three of them are back.

Serena Williams beat her older sister Venus Williams in the final to capture an Open era-record 23rd major here last year but decided against defending her title because she didn't have enough time to recover from health issues after a complicated childbirth in September.

Venus Williams is seeded fifth and is the second match scheduled on centre court to get her 77th major under way with a challenging opener against Belinda Bencic.

She's 4-0 in career head-to-heads against 20-year-old Bencic, who reached a career-high No 7 ranking in 2016 and helped Federer win the Hopman Cup title for Switzerland earlier this month. But she has had an abbreviated preparation that included a loss in the second round to eventual champion Angelique Kerber at the Sydney International last week.

At 37, Venus Williams is among the top contenders at Melbourne Park. Others in action tomorrow include seventh-seeded Jelena Ostapenko, who meets Francesca Schiavone in a match featuring current v former French Open champions, No 2-ranked Caroline Wozniacki, who opens against Mihaela Buzarnescu, and US Open champion Sloane Stephens against Zhang Shuai.

Simona Halep is the No 1 seed in the women's draw and one of six women who can hold the No 1 ranking at the end of the Australian Open. Halep, who has had back-to-back first-round exits on her last two trips to Melbourne Park, opens on day two against Australian wild-card entry Destanee Aiava.

Only two men can hold the top ranking in the first week of February, Nadal or Federer, regardless of what No 3 Grigor Dimitrov, No 4 Alexander Zverev or anybody else does in Melbourne.