Sabalenka, A four time major winner, raced 5-0 clear of qualifier Bai Zhuoxuan, ranked a lowly 702, on centre court before wobbling to give the Chinese player a glimmer of hope.
But the top seed quickly snuffed it out to race home 6-3, 6-1 and set up a clash next with Russian-born Anastasia Potapova, now representing Austria, who dispatched 2021 US Open champion Emma Raducanu.
“Super-happy to close the (first) set, it gives me confidence that my game is there, my focus is there,” said Sabalenka, who is bidding for a third Australian Open title in four years.
“Step by step. Super-happy with my win. There is always a little gap to improve.”
Sabalenka has only dropped nine games to date, as she looks to make amends for her upset in last year’s final to Madison Keys.
Third seed Gauff was clinical against Serbia’s Olga Danilovic, who ended Venus Williams’ tournament in round one. The two-time major winner took just 78 minutes to race home 6-2, 6-2 on Margaret Court Arena.
It set up a showdown next against fellow American Hailey Baptiste, ranked 70, who downed home hope Storm Hunter in straight sets.
“Near perfect,” said Gauff, whose best performance in Melbourne was a semi-final in 2024.
Ukrainian 12th seed Elina Svitolina, Turkish prospect Zeynep Sonmez and in-form Canadian teenager Victoria Mboko also won on day four, all sweeping past their opponents in straight sets.
The Men section included three-time finalist Daniil Medvedev who, too, remained alive, but needed four sets to keep his Grand Slam dream on track at a cooler, overcast Melbourne Park after days of hot weather.
Spanish superstar Alcaraz powered through a grueling arm-wrestle 7-6 (7/4), 6-3, 6-2 on Rod Laver Arena against hard-hitting German Yannick Hanfmann as he continued his journey to a career Grand Slam. But he was put through his paces by a player 12 years older before setting up a showdown with either France’s Corentin Moutet or American Michael Zheng.
“To be honest, it was tougher than I thought at the beginning,” said Alcaraz, who already has six major titles but has never gone past the last eight in Melbourne.