'Super disappointed' Osaka comeback ended by big-serving Pliskova
Pliskova, who won the tournament the last time it was held in 2020, bounced back from losing the first set to grind down the Japanese star 3-6, 7-6 (7/4), 6-4 in the second round.
World number two Aryna Sabalenka, meanwhile, thumped Italian Lucia Bronzetti 6-3, 6-0 in a dominant display on Pat Rafter Arena.
"Even though it's super disappointing today, I know that if I keep training and if I keep putting in the work, then I'll eventually get to where I want to be," said Osaka.
"It's kind of tough because she has such a great serve -- my break points could have been better, but I think other than that, we both played really well.
"Even stepping on the court is a personal win because a couple of weeks ago I was even doubting if I could play with everyone," she added.
"So I guess these two matches that I've had kind of prove to me that I am doing okay, and the year is just going to get better for me."
The four-time Grand Slam champion had not played a tournament since September 2022, citing mental health concerns. She had a baby daughter in July before deciding to make a comeback.
After an impressive first-round win over Germany's Tamara Korpatsch, Osaka started strongly against the 39th-ranked Pliskova, breaking the Czech's opening service game.
Pliskova, a two-time Grand Slam finalist, levelled but Osaka broke again to take a 4-2 lead then held on to bank the opening set.
The momentum began to shift in the second set as the tall Pliskova began to find the mark with her serve.
She won the second set tiebreak then got an early break in the third, holding on with ease to take the match in 2hr 13min.
Pliskova has won the Brisbane International three times and said she felt better and better as the match progressed.
"I thought I played quite well -- there are a lot of things to improve but it's a good start," said Pliskova, adding that after a first-round bye and having not played since September, she needed time to find her feet.
"You can practise as much as you want but in matches it's always a little bit different," she said.
Reigning Australian Open champion Sabalenka was in imperious form against Bronzetti, breaking the Italian once in the first set and three times in the second.
"I'm super happy with the performance and I think I played a really great match," said Sabalenka, who won 24 points to Bronzetti's five in the second set.
"I just hope I can keep this same level for each match, or even better.