Kvitova, who slumped to 29 in the world after being attacked in her home by a knife-wielding man in 2016, has battled her way back to number eight and was encouraged by her 6-1, 7-5 win over the Belarusian.
Sabalenka is a form player, racing to number 11 in the world after a stellar 2018 and starting the year by winning the Shenzhen Open.
"She was definitely (finishing strongly). She came from Shenzhen (last week) where she won the tournament so I knew it would be a tough match," said Kvitova.
"Unfortunately I lost (to her) at the US Open but I'm happy with my performance here in the first round.
"It's always tough to play her, she's a big server, big hitter. So I'm really happy that I was able to win it." Kvitova belted 28 winners to Sabalenka's 11 and won an incredible 85 percent of her first-serve points during the 79-minute contest.
She is aiming for her second Sydney title after lifting the trophy in 2015.
"I just hope that I can continue and enjoy tennis in this season," said the Czech, who won five WTA titles to return to the top 10 in 2018.
"It's great coming somewhere where you really love, of course, when you win a title it's something very special in your heart." There was no such joy for Romania's Ostapenko, whose poor form continued in a 6-3, 6-3 defeat to Barty.
Last year Muguruza was the top seed and world No.2, but 12 months on she is unseeded and down to 18.
"But, hey, it's competition, so we have to put poker face and try to win." In the men's draw Australian teenager Alex De Minaur, a finalist last year, continued his preparations for the Australian Open with a 6-4 6-3 win over Dusan Lajovic.
Towering Americans Sam Querrey and Reilly Opelka are also through to the next round.
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