With the tees moved up from the posted championship yardage and the par-72 Meadow Course playing to 6,526 yards, the long-hitting Yin took full advantage. The thin mountain air also played to her favor, with the Arcadia High rising junior belting some of her drives 300 yards.

“The par 5s, I could reach them because they’re shorter,” said Yin, who made the cut at this year’s Kraft Nabisco Championship on an amateur exemption. “It was pretty short for me.”Starting on the 10th hole, Yin’s first nine holes included three birdies and two bogeys. She then lit up the second nine, converting five birdies in closing with a 5-under 31.

“I started getting more warmed up,” said Yin, who teed off at 7:20 a.m. MST with temperatures in the mid 50s. “The morning was actually pretty cold.”

Arizona seems to bring out the best in Yin. This is the third time she has returned a 66, her lowest competitive round, in an Arizona-based event. She shot a 66 in the second round of the 2012 Joanne Winter Arizona Silver Belle Championship, held at Whirlwind Golf Club in Chandler, as well as in the first round of the 2012 Winn Grips Heather Farr Classic, held at Longbow Golf Club in Mesa.

Mariel Galdiano, 16, of Pearl City, Hawaii; Megan Khang, 16, of Rockland, Mass.; and Jennifer Kupcho, 17, of Westminster, Colo., share second at 3-under 69.

“This golf course is in great shape,” said Khang, who fell to eventual champion Gabriella Then in the semifinals of the 2013 Girls’ Junior. “We’re playing it long, but it does make up for the distance in the change of altitude here.”

Khang, who last month played in her second U.S. Women’s Open, is the ninth player to compete in six U.S. Girls’ Juniors. She has taken a fair amount of playful ribbing from her fellow competitors over that statistic.

“I’m not technically old yet, but I’m being told that I’m old,” said Khang, who is one appearance shy of the championship record of seven set by Margot Morton (1954-60).

Six players are tied for fifth at 2-under 70, led by three-time Mexican Amateur champion Marijosse Navarro, 17, of Mexico. Local favorite Hannah O’Sullivan, 16, of Paradise Valley, Ariz., opened with a 1-under 71 and is tied with four other for 11th.

Eun Jeong Seong, the runner-up and record-setting stroke-play medalist at last week’s U.S. Women’s Amateur Public Links, showed early signs of understandable fatigue. But after opening with bogeys on three of her first five holes, she made birdies at Nos. 1-4 (her 10th-13th) and finished at even-par 72.

Andrea Lee, who made the cut at the 2014 Women’s Open, carded a 2-over 74. Her fellow Women’s Open competitors Kathleen Scavo and Bailey Tardy opened with 73 and 75, respectively.

The 2014 U.S. Girls’ Junior Championship consists of 36 holes of stroke play followed by six rounds of match play. The championship is scheduled to conclude with a 36-hole final at 9:30 a.m. MST on Saturday.

The U.S. Girls’ Junior is one of 13 national championships conducted annually by the United States Golf Association, 10 of which are strictly for amateurs.

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