Sabalenka sets up potential Raducanu showdown at Australian Open
The world number one saw off the awkward Bai 6-3, 6-1, having threatened at one stage to complete the job in even more express fashion.
Britain's 2021 US Open champion Raducanu plays Russia-born Austrian Anastasia Potapova later Wednesday at Melbourne Park, with Sabalenka lying ominously in wait.
Sabalenka is favourite to win a third Australian Open in four years, having been defeated in the final 12 months ago by Madison Keys.
"Tricky opponent," said the Belarusian.
"Super-happy to close the (first) set, it gives me confidence that my game is there, my focus is there.
"Step by step. Super-happy with my win. There is always a little gap to improve."
Sabalenka won the first nine points in a row to surge into a 2-0 lead at Rod Laver Arena against her outclassed opponent ranked 702 in the world.
After just eight minutes it was 3-0, then 5-0, with Sabalenka seemingly intent on getting the job done in time for an early lunch.
But the 23-year-old Bai, playing the biggest match of her life, worked through her nerves and finally held serve.
She then stunned centre court by breaking Sabalenka's serve to reduce the deficit to 5-2, and doggedly held her own serve for 5-3.
The 27-year-old US Open champion Sabalenka was beginning to show signs of frustration as she saw numerous set points come and go.
She finally got the job done after 39 minutes on her seventh chance, slamming a ball she was holding in her hand down on the court in a flash of anger.
The second set was more serene, Sabalenka's superior power taking its toll as she sealed the match in 72 minutes.