It brought to an end another bid to equal Margaret Court’s record Grand Slam haul for Williams
Serena blamed her defeat on “a big error day”.
Osaka won 6-3 6-4 as Serena’s quest to reach a ninth Australian Open final and match Court’s 24 major singles titles.
“The difference today was errors. I made so many errors.
“Honestly, it was opportunities where I could have won. I could have been up 5-0. It was a big error day for me,” Williams 39, said.
When pressed on what caused her to make so many mistakes, tears began to flow as she told reporters: “I don’t know. I’m done,” before walking out.