No. 2 Sabalenka, who won her first Grand Slam title here last year, beat Amanda Anisimova 6-3, 6-2, while Gauff, who picked up her first major at the US Open in September, crushed Magdalena Frech 6-1, 6-2.
Anisimova had won four of their previous five meetings, but the American was powerless to stop the power of the Belarusian player, who hit 18 winners.
“I’m super-happy with the level, happy to get this win, she’s a tough opponent,” Sabalenka said. “I love the atmosphere here. I love playing in front of you guys. I really want to stay as long as possible, and hopefully we can get this thing one more time.”
A brief rain delay at 4-1 in the first set stopped Sabalenka’s momentum, but she quickly regrouped and pulled away in the second set. She will meet Barbora Krejcikova in the last eight after the No. 9 seed defeated 16-year-old Russian player Mirra Andreeva 4-6, 6-3, 6-2. Andreeva had been bidding to become the youngest Australian Open quarterfinalist since Martina Hingis in 1997.
Gauff was the first woman through, needing just 63 minutes to see off Frech in a match played on Rod Laver Arena in front of the man himself.
“Luckily when I saw him come in I was already well up,” Gauff said. “I heard clapping and knew it wasn’t for us, it was only the first set. But thank you for coming. It’s an honor.”
Still a teenager, Gauff drew attention to her shoes, which carry a number of messages, including one that says: “you can change the world with your racquet,” something her father told her as a little girl.
“Sometimes when my mom thinks I’m negative when I look down, I’m just looking at my shoe, just a reminder that life is much more than tennis, how I do on the court does not define me as a person,” she said. “That goes for everyone. Your workplace, whatever you do, doesn’t define you as a person. Just surround yourself with good people. Everything I do on court is a plus to my life. I have everything I need. This is just all extra.”