South Korean Ryu kept making birdies in a bid to post her lowest round on the LPGA Tour. She accomplished that on Friday with a 10-under 62 that gave her a six-shot lead.
Ryu had a run of four straight birdies on the front nine and the back nine at the TPC Boston despite its small targets and firm greens. And she had a simple explanation for them.
"Just an amazing day because my shots, everything next to the hole. And my putts, everything get in the hole," said Ryu, the 23-year-old who was LPGA rookie of the year last season. "Amazing day, yeah."
Even more amazing was the size of her lead. Ryu was at 13-under 131, with Bianca Pagdanganan, Yealimi Noh and Choi tied for second at seven under. Pagdanganan had a 66, and Noh and Choi each shot 68.
Choi, the 26-year-old from Sydney, had six birdies to go with two bogeys.
Jin Young Ko (67) and US Solheim Cup player Lauren Coughlin (69) were at six under.
Marina Alex, who had the 18-hole lead after a bogey-free 68, followed that with a 72 and is nine behind.
Birdie runs are nothing new for Ryu, a five-time winner on the Korea LPGA before earning her LPGA card as the medallist at its Q-Series. She won the Walmart NW Arkansas Open last year with a 29 on the back nine.
She started her big run with a birdie on the par-4 fourth and then birdied the next three holes to seize control. She had two birdies in three holes to start the back nine, and then made four in a row starting on the 14th hole.
Ryu was hitting it so well she thought she might have holed out for an eagle on the par-4 15th because of the cheer. Turns out there was one person in her cheering section that might have been over the top for a ball that settled about four feet away.
"My mom's reaction is almost getting the eagle, but the ball still on the green," Ryu said. "Just fun facts for today. My mom is really happy ... just the ball is next to the hole. Yeah, just for 10 seconds I just think, 'Oh, I got an eagle.' Just birdie."
The 62 was her low round by two shots on the LPGA. She previously had rounds of 64 on three occasions.
Australian Hannah Green made a big improvement on her first-round 74 with a 69.
The 2019 Women's PGA champion is now tied 31st at one under, one ahead of compatriot Grace Kim.
Kim (68) improved drastically with a flawless second round capped by four birdies after her opening 76.
