The Japanese star has struggled for consistency since returning to the court a year ago after the birth of daughter Shai in July 2023.
Now ranked 57, she stressed on Sunday that the fire to win still burned brightly and she was confident of revisiting her former glories.
Now under the wing of Serena Williams' long-time coach Patrick Mouratoglou, the 27-year-old put in a solid performance at the Auckland Classic to overcome Israel's Lina Glushko, ranked 221, 6-4, 6-4.
But she to dig deep with Glushko making her work hard in the rallies.
Osaka converted the only break point she had in a tight first set and raced to a 3-1 lead in the second.
But Glushko then reeled off three games in a row before Osaka regrouped to win the next three in windy conditions for the 85-minute victory.
She will next play either Spanish qualifier Leyre Romero Gormaz or Austria's Julia Grabher in the next round.
In other action, fellow Japanese player Nao Hibino outlasted Germany's Jule Niemeier 6-3, 6-4 while Dane Clara Tauson beat Italy's Lucrezia Stefanini 6-2, 6-3.
Top seeds Madison Keys and Elise Mertens begin their campaigns on Tuesday, as do former Grand Slam winners Emma Raducanu and Sofia Kenin.
