Most players would be content to rest the day before a big match, but not Serena Williams.

The 23-times Grand Slam champion said she had to step in to avert an "emergency" at her clothing line on Saturday, a day ahead of her Australian Open last 16 match against Aryna Sabaleka.

Williams, who beat the Belarusian 6-4 2-6 6-4 to reach the quarter-finals, said the situation was "so crazy".

"As CEO, I had to kind of step up a little bit. I was on the phone with our designer making final orders and deciding how much fabric we need for our new collection," she added.

"It was almost a mind trip because I was like, 'Oh my gosh! We have to play tomorrow but we've got to get this done. Business keeps going.'"

Williams has earned about $94 million in career prize money and is also an investor in more than 50 startups, focusing on firms started by women and minorities.

Finding time for two careers as well as her daughter, Alexis Olympia, can be challenging, she said.

"I scheduled the call directly after my practice," she added.

"I was like, 'Okay, I can do it early and still have the rest of the day to relax.' And it was during Olympia's nap, so it was perfect.

"Tennis is a lot less stressful.

"I think a part of me loves being on the court because it's free-flowing.

"It's not like I have to kind of just manage and make sure everyone is able to perform. But that's what I do. I have a second career, and it's fun."

Williams next faces either Simona Halep or Iga Swiatek.