Sabalenka said she was relishing the match against Osaka, while adding it is great to see her showing signs of the form which made her a four-time Grand Slam champion.
Osaka won the US Open and Australian Open twice between 2018 and 2021 but did not play for 14 months around the the birth of her daughter Shai in July 2023.
“It’s great to see her back on her level. Maybe not at her best level, but she’s back, she’s fighting, she’s building her level,” said Sabalenka.
“I feel like I really enjoy our battles. It’s high-level matches, and I really enjoy when somebody pushes me to the limit.”
Sabalenka took control of her match early, winning 92% of first-serve points in the opening set as Kasatkina failed to win a game.
Kasatkina improved in the second set as she broke to briefly lead at 2-0, but Sabalenka broke back immediately before asserting control late on and converting the second of three match points.
Victory means Sabalenka is the ninth woman to win 100 matches while ranked number one in the world.
Joining Sabalenka and Osaka in the last-16 is France’s world number 92 Diane Parry, who stunned American sixth seed Amanda Anisimova.
Parry, 23, won 6-3 4-6 7-6 (10-3) to reach the fourth round of a Grand Slam for the first time, while Anisimova’s wait for a maiden Grand Slam title goes on.
Parry was serenaded by the home crowd on an electric Court Philippe Chatrier and had to wait for them to stop singing before she could conduct her post-match interview.
She will face Polish qualifier Maja Chwalinska in the fourth round after her 1-6 6-3 6-2 victory over Greece’s Maria Sakkari.
