Turning 40 in September, Williams's latest quest to match Margaret Court's all-time record of 24 grand slam singles crowns ended in a shattering 6-3 6-4 loss to Osaka on Thursday.

With her hand on heart, the American paid a touching tribute to the crowd before leaving Rod Laver Arena, raising the prospect that her 21st Open campaign may have been her last.

"I don't know. If I ever say farewell, I wouldn't tell anyone," Williams said.

"So ..: I don't know. The Aussie crowd is so amazing, so it was nice to see."

Williams has been stranded one shy of Court's record since capturing her 23rd grand slam title at Melbourne Park four years ago with victory over her older sister Venus while three months pregnant with her daughter Olympia.

The 39-year-old has since suffered four grand slam final defeats - two at Wimbledon and two at the US Open - and was left devastated by her straight-sets loss to Osaka.

"The difference today was errors. I made so many errors," Williams said.

"Honestly, it was opportunities where I could have won. I could have been up five-love. I just made so many errors."

Twenty-four in fact, to just 12 winners.

Asked how she hoped to juggle tennis with travel and motherhood during the ongoing pandemic, Williams was in no mood to reveal her plans.

"I feel like I haven't really thought about that so much," she said.

"But I think going through last year with the pandemic was definitely interesting. So I have a little experience under my belt with that, I guess.

"But, yeah, those are things that I haven't really thought about."

Then, breaking down in tears, the seven-times Australian Open champion cut short her post-match press conference.

"I don't know," Williams said. "I'm done."

Osaka, for one, grew up idolising Williams and certainly hopes Williams' grand slam career isn't close to done, too.

"It's kind of sad when you say it like that because, for me, I want her to play forever," Osaka said.

"That's the little kid in me.

"I was a little kid watching her play and just to be on the court playing against her is a dream.

"I felt it's like always a surreal moment, just to see her in real life, like close up, because I rarely see her, to be honest."

Australian Samantha Stosur - herself closing in on retirement - doesn't believe Williams needs to catch, or surpass Court's grand slam record, to validate her standing as women's tennis' so-called GOAT - greatest of all time.

"She's the greatest player anyway," Stosur said on Thursday.

"I think many players would already think that and argue that fact regardless of whether she gets this 24th title or not."

Australian Associated Press