An aging Serena Williams aims for a 24th Grand Slam title, four years after her last, faced with an ever-growing coterie of young talent taking over at the top of the game.
Here are five women to watch at the Australian Open, which starts on Monday after a three-week delay because of the coronavirus:
Osaka picked up her third Grand Slam at the 2020 US Open, coming from a set and a break down to beat Victoria Azarenka in the final, and won widespread praise for her passionate support of the Black Lives Matters movement.
Named one of five sportspersons of the year by Sports Illustrated, the Japanese world number three, who also has Haitian heritage, wore different masks honouring victims of systemic racism and police brutality in the United States in each of the seven rounds at Flushing Meadow.
Media and officials in Japan broadly welcomed Osaka's campaigning. Public broadcaster NHK broke into its news programme to flash the news of the 23-year-old's latest Grand Slam triumph.
She became the first Asian player to become world number one after backing up her maiden 2018 US Open win with Australian Open victory in January 2019.
She fell in the last 32 at Melbourne Park a year ago to teen sensation Coco Gauff, before turning the tables on her 15-year-old opponent in New York.
Despite hardly swinging a racquet for the best part of a coronavirus-ravaged year, world number one Barty still managed to make sporting headlines in 2020.
In September the multi-talented Australian, a former professional cricketer, won a golf tournament near Brisbane.
And, as a passionate fan of the Richmond Tigers Australian Rules Football team, she was delighted to award Tigers skipper Trent Cotchin the trophy after Richmond won the sport's Grand Final in October.
Barty claimed her maiden Grand Slam at Roland Garros in 2019 but did not defend her French Open title as she missed all post-pandemic shutdown tournaments citing health and travel risks.
She had started 2020 in top form, winning her maiden title on Australian soil at Adelaide before losing a heartbreaking Australian Open semi-final 7-6 (8/6), 7-5 to eventual champion Sofia Kenin.
Every year since 2017 the question has been the same: can Williams pull level with Margaret Court as a 24-time Grand Slam champion?
But the truth is now that time is against the US superstar who will turn 40 in seven months' time, having limped out of the French Open with an Achilles injury in September -- making 2020 the first year since 2006 that she failed to reach a major final.
Her last Grand Slam triumph came in Australia four years ago, and since when she has lost twice in the finals of both Wimbledon and the US Open.
Currently ranked 11, her best Grand Slam showing during a stop-start 2020 was her semi-final run at the US Open, where she lost to Azarenka in three sets.
Pregnant during her 2017 triumph in Australia, a relaxed Williams enjoyed her first day out of quarantine last week by taking her now three-year-old daughter Olympia to Adelaide Zoo.
"We promised that we would take her to see koalas and kangaroos."
Defending champion Kenin did not come into the Melbourne warm-up week completely cold, having reached the quarter-finals in Abu Dhabi last month where she lost to Greece's Maria Sakkari.
Kenin's hopes of book-ending her breakthrough 2020 season with a second major at Roland Garros were dashed by injury as Iga Swiatek ran away 6-4, 6-2 to win a shock French Open title.
The 22-year-old's left thigh was taped early in the second set and she failed to win another game in her first final on clay.
Kenin ended the year at a career high fourth in the rankings and was voted WTA Player of the Year.
Small in stature but big on fighting spirit, Kenin memorably edged world number one and home favourite Barty in the Australian Open semi-finals a year ago.
In the final, the 14th seed had to dig deep at three break points down in the third set against Garbine Muguruza, hitting five consecutive winners to take a decisive 3-2 lead.
Kenin said she almost burst into tears during the changeover at 5-2 before controlling raging emotions to close out her first Grand Slam.
"I sat down, tried not to cry in front of the world, but inside I was like, oh, my God, am I about to win?"
Former world number one Halep goes into the tournament celebrating seven consecutive years and 347 weeks ranked inside the top 10, placing the two-time Grand Slam champion in some exalted company.
The Romanian's streak is the eighth best in WTA history.
The only players to have spent more weeks continually in the top 10 are all-time greats Martina Navratilova, Chris Evert, Steffi Graf, Gabriela Sabatini, Pam Shriver, Arantxa Sanchez and Hana Mandlikova.
Since bursting into the top 10 in January 2014, the supremely consistent Halep has won 16 tournaments, tying with Petra Kvitova for the most during that time, including the 2018 French Open and 2019 Wimbledon.
Now the world number two would dearly love to add an Australian Open, having come agonisingly close three years ago when losing an epic final 8-6 in the third set to Caroline Wozniacki.
She threatened again last year before being edged out 7-6 (8/6), 7-5 in the semis by Muguruza.
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