The former world No. 1 prevailed 6-3, 7-6(4) in a challenging encounter, overcoming a second-set fightback from the Italian to secure her place in the next round.
Osaka will now meet Mia Pohankova, who progressed after defeating Tereza Valentova on Tuesday. Victory in that encounter would set up a meeting with either Alycia Parks or Kimberly Birrell, with a place in the semi-finals at stake.
The Japanese star made a strong start against Paolini, breaking early to establish a 3-0 advantage. However, her opponent responded by winning three consecutive games to draw level.
Osaka regained the initiative, moving 5-3 ahead before breaking Paolini again and serving out the opening set 6-3.
The second set proved considerably tighter. Osaka edged in front at 3-2, but Paolini turned the contest around to lead 4-3 before moving within a game of forcing a decider at 5-4.
The Italian earned three set points but was unable to take advantage of her opportunities, allowing Osaka to recover and force a tie-break. Osaka then held her nerve to claim the tie-break 7-4 and complete the victory.
The result marks an encouraging start to Osaka’s campaign at her annual return to Japan. She is competing in only her second tournament since the US Open, having reached the last 16 in Beijing earlier in the year. There, she defeated Maria Timofeeva and Sara Bejlek before falling to Karolina Muchova.
