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 revived the JLPGA Tour after the retirement of Ayako Okamoto, over 32,000 spectators, the largest gallery ever to attend a JLPGA event, witnessed the final round.
At the LPGA Qualifying Tournament in Florida in December 2005, Miyazato easily secured her tour card for the 2006 season. She was under-par in four of the five rounds, and was 12 strokes ahead of the closest competitor, which set a record for the largest margin of victory. Back in Japan, on 15 December, 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.