In winning the Japan Open Championship at age 20 in 2005, Miyazato became the youngest player on the JLPGA Tour to win a major. Furthering the notion that Miyazato has revived the JLPGA Tour after the retirement of Ayako Okamoto, over 32,000 people, the largest gallery ever to attend a JLPGA event, witnessed the final day of that tournament.
She dominated the 2005 U.S. LPGA Q-School and secured her tour card, enabling her to compete in the 2006 season. She finished under par for four of the five qualifying rounds, and finished 12 strokes ahead of the closest competitor, setting a record for the largest margin of victory. Back in Japan, on December 15, she played the opening rounds of the Okinawa Open, becoming the first Japanese woman to compete in a domestic men's professional event, although she failed to make the cut for the final rounds.
Miyazato earned her first LPGA Tour win at the 2009 Evian Masters, shooting 14-under par 274 to tie Sophie Gustafson who she then beat on the first playoff hole.
In 2010, she won four of the first nine official tournaments on the LPGA Tour and on 21 June rose to number 1 in the Women's World Golf Rankings. She held the spot for only one week and was replaced by Christie Kerr who held the spot for three weeks, before Miyazato regained the spot again on 19 July, by a margin of 0.0006 average points.
