Krueger hadn't dropped a set at the tournament leading into Sunday's final, and the 19-year-old Texan showed few nerves as she broke No. 35-ranked Zhu's first service game of the match and then maintained composure through a tight second set and tiebreaker to claim her breakthrough title in 1 hour, 36 minutes.
Before this week, the 123rd-ranked Krueger's best tour result was the quarterfinals on the grass of 's-Hertogenbosch. She came into the week without a main-draw win on hard courts this year.
Her victory in Osaka will move the American inside the top 100 for the first time.