Sabalenka faced American Sloane Stephens, the 2017 US Open champion, under the roof at Rod Laver Arena on a rain-marred day and posted a 6-3 6-2 victory.
While she never appeared in danger of defeat, the world No.1 lacked her usual polish, with her booming serve going missing while unforced errors at times caused her headaches.
She roared to a 4-0 lead in the first set but then twice dropped her serve to allow Stephens to claw her way back to trail 4-3.
Sabalenka was able to break the world No.66 and then was able to serve it out.
The 26-year-old again took a commanding lead in the second set and this time was able to maintain her focus to wrap up the win in 71 minutes, handing Stephens her eighth straight defeat since Wimbledon.
But with only two aces for the match, just 70 per cent of first serves finding the mark and 21 unforced errors, Sabalenka acknowledged there was work to do.
"It was not like I played my best but I'm just glad I was able to close it out in straight sets," she said in her on-court interview.
Sabalenka is bidding to become the first player since Martina Hingis in 1999 to complete a Melbourne Park hat-trick.
She will face Spaniard Jessica Bouzas Maneiro in the second round.
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