With the men's world number one Novak Djokovic flying home after being denied entry to defend his title, the tournament remains wide open with Rafael Nadal, Alexander Zverev, Daniil Medvedev and Stefanos Tsitsipas all in contention.
The Australian Open has finally begun at Melbourne Park after a chaotic and controversial build-up dominated by the visa saga that engulfed world number one Novak Djokovic.
On Monday, Germany's Tatjana Maria struck the first serve of the opening Grand Slam of the year on Rod Laver Arena against Greece's Maria Sakkari, the fifth seed, in the women's singles.
Defending champion Naomi Osaka follows her on centre court with 20-time Grand Slam winner Rafael Nadal concluding the afternoon action on an overcast and cool day, with crowds capped at 50 percent capacity due to coronavirus.
World number one Djokovic was supposed to be the headline act in the night session, but the unvaccinated Serbian is not defending his title after a court threw out his bid to stay in the country.
The 34-year-old flew out of Australia on Sunday night, his dreams of becoming the first man to win 21 majors over, at least for now, gifting Nadal the chance to instead be first to reach the milestone.
Tournament wide open for Nadal, others
With Djokovic missing, third seed Alexander Zverev was instead elevated to Rod Laver Arena to conclude the day's action with his clash against fellow German Daniel Altmaier.
World number one Ashleigh Barty's showdown with qualifier Lesia Tsurenko opens the evening session.
Fifteenth seed Elina Svitolina of Ukraine began proceedings on the neighbouring main show court, Margaret Court Arena, against Fiona Ferro of France.
With nine-time Australian Open champion Djokovic missing, the men's tournament is wide open with Nadal, Zverev, US Open champion Daniil Medvedev and Greek world number four Stefanos Tsitsipas all in contention.
But there is no Roger Federer this year, with the Swiss great battling injury.
Ashleigh Barty is favourite
Barty is the firm favourite on the women's side to win her home Slam for the first time, but will be under intense pressure from an expectant crowd.
Osaka, seeded just 13 after a long layoff to deal with mental health issues, will need to topple the Australian if she is to make it a hat-trick of titles in Melbourne.
Serena Williams is not in Melbourne because of fitness concerns.