Ai Miyazato said Monday her struggles to stay motivated triggered the decision to retire at the end of the season, something she has been trying to overcome the past five years.

The 31-year-old Miyazato said she made her decision to call it a career last summer.

"I tried to find a way to get over them," Miyazato said at a press conference. "I've been talking to my mental coach as well, but not being able to get the motivation back made it difficult to keep chasing my goals."

"I had three weeks off last August because of the Olympics. I never had a break that long at that time of the year since I turned pro, and that gave me the time to think about my future. I always had something on the back of my mind, but those three weeks gave me the opportunity to organize my thoughts."

Miyazato has won nine titles on the U.S. LPGA Tour, the second most by a Japanese. She won five tournaments in 2010 when she rose to No. 1 in the world rankings, a position she held for 11 weeks.

Miyazato, however, said the fact that she could not win a major despite being at the top of her game started to trouble her.

"I was winning titles for four years but not in the majors, and I started to wonder what next if I can't win when I'm at my best," she said. "I lost my way and it was really difficult to get things back on track."

"(Losing motivation) was due largely to reaching the top of the rankings. But I still have the chance to compete in majors this season, and I feel like I can give it one, final push toward the end. I'll give it everything I have left."

GALLERY: Golfer Ai Miyazato formally announces retirement

The youngest member of a golfing family from Okinawa, Miyazato in 2003 became the first amateur in 30 years to win on the professional circuit at the Dunlop Ladies in Miyagi Prefecture, where she was attending high school -- a moment she referred to as a turning point in her life.

"I wouldn't be who I am without that tournament," she said. "I've never thought I'd turn pro while being a high-school student and I'm so thankful for the time I spent in Miyagi, where I have lots of memories and people who support me even after the (March 11, 2011, earthquake and tsunami) disaster."

Miyazato spiked the popularity of women's golf in Japan after making her pro debut in 2004, winning five Japanese LPGA tour titles and becoming the first teenager on either the men's or women's circuit to earn 100 million yen in a season.

Miyazato, who has won 15 titles on the domestic tour, headed stateside in 2006 and won her first event in her fourth LPGA season at the 2009 Evian Masters in France, defeating Sophie Gustafson on the first hole of a sudden-death playoff.

"In the United States, the first win at the Evian (is most memorable). That was fulfilling as it took four years," she said. "I was in a slump before that, and a tee shot on the 18th was the moment I got over the hill."

Fluent in English, Miyazato also paved the way to the United States for her compatriots including Mika Miyazato, Momoko Ueda and Sakura Yokomine. She offered some advice for those hoping to follow in her footsteps.

"I'm one of the smaller golfers on the U.S. tour. I don't have power either, but I made up for it by honing my accuracy and techniques and I had the mental training helping me, too, all of which became the base for my game," she said. "If I could do it, so can others, too."

"I only had a handful of chances to play with the current young players, but they really have the technique as well as the physical game. Part of the game get more difficult older you get but I want them to stick to their belief."

Miyazato's last victory on the LPGA Tour came at the NW Arkansas Championship in 2012. Miyazato's best finishes at the majors were third at the Women's PGA Championship (2006, 2010) and the Women's British Open (2009).

Her form has dipped in recent years as she currently ranks 115th in the world, and she has not finished higher than 34th in five competitions this season. She said the timing to call it a career is not too early, referring to former world No. 1s Lorena Ochoa and Annika Sorenstam as an example.

"Lorena's retirement was a real shock that came out of the blue, but she was cool right until the very end," Miyazato said of the Mexican. "She was a sporting figure that represented Mexico, but she was true to her mind."

"The same goes for Annika, everyone has her moment to draw the curtain."

Miyazato said she plans to play at the tournament where she won her first LPGA title.

"I haven't decided which tournament will be my last, but will head back to the U.S. tour after the next tournament in Japan and am hoping to play at least until the Evian," she said.