Uchijima, playing in the second round of a Grand Slam tournament for the first time, could not cope with Sabalenka's powerful serve and groundstrokes.
The Belarusian wrapped up victory in 62 minutes and will next face her good friend Paula Badosa in the third round.
While most matches on the outer courts were suspended due to rain once again, Sabalenka said she was fortunate to be among the top seeds which guarantees matches under the roof if required.
"That's the little advantage we get as top players because we play in the big stadiums with the roof. So I knew that no matter what the weather is going to be, I'm going to play my match. That's really helpful," Sabalenka said.
"It helps to manage the energy because it's really tough when the weather is like that and you play on the outside courts. It just feels like you're wasting your energy during the day going on and off the court. That's really tough."
Sabalenka won six points in a row at the start of the match but once Uchijima had overcome her nerves she gained confidence and settled down against the Belarusian.
Uchijima held her serve but when she trailed 3-2, Sabalenka had warmed up and she pounced on a break point with a fierce winner before taking the first set in 29 minutes.
The two were meeting for the first time but Sabalenka said she had done her homework after her team provided her with videos of the Japanese number one.
"I watched her previous matches, we had all the videos. I'd say I knew a lot about her going into this match," Sabalenka said of Uchijima, who is ranked 83 in the world.
Uchijima wore a sombre expression during the changeover before the second set and she had no answer to the power of Sabalenka who also showcased her variety by approaching the net and playing some telling drop shots.
Uchijima afforded herself a smile when she got the better of the Belarusian on a long rally to make it 4-2 but Sabalenka refocused to save a break point before breaking the Japanese player's serve to seal victory.
"It was definitely fun playing all those drop shots. Super happy with the result and I really enjoyed playing today," Sabalenka added.
