Ko, a 15-year-old phenom who is still classified as an amateur, fired her second straight 4-under-par 68 to grab a share of the second-round lead with four-year LPGA veteran Chella Choi. Both Ko and Choi sat at 8-under 136.
Ko, who was born in South Korea but has called New Zealand home since she was a tyke, continued a torrid season in which she has already won the U.S. Women's Amateur and a professional tournament in Australia. The Grade 11 student went bogey-free as she played the front nine in even-par and shot 4-under on the back.
Ko indicated she was not feeling as much pressure as her more seasoned competitors were.
"I'm just here for the experience," she said. "But the professionals, on the other hand, it's about how much money they're going to get by each placing."
Meanwhile, Jessica Shepley of Oakville, Ont., was the lone Canadian to make the cut. She made a bogey-saving on the 18th hole to finish with a two-over 74 that placed her right on the cut line of 147.
"Obviously, that's not what I was looking for — to have a 10-foot downhill, left-to-right slider on 18 to make the cut," said Shepley. "But it went in, so that's all that matters."
However, veteran Lorie Kane of Charlottetown experienced heartbreak as she double-bogeyed her final hole and was one shot above the projected cut of 147. Kane finished with a 4-over 76 to follow an even-par opening round.
"That's not the way I wanted to finish, and I worked very hard today and grinded hard," said Kane. "Unfortunately, I'm kind of feeling like (disqualified 2012 Canadian Olympic relay runner) Jared Connaughton right now, like I touched the line."
Ko, who hopes to turn pro in a couple of years and also dreams of attending Stanford like her favourite golfer Michelle Wie, moved up from a first-round share of third place. Meanwhile, Choi, also a South Korea native, charged up the leaderboard with a sizzling 8-under 64. It was a big improvement from the first round, when she only managed an even-par 72 and found herself in 32nd place.
Choi, who turns 22 on Saturday, said she was suffering from a sore shoulder in the first round, but a massage treatment paid off.
"I'm very happy," she said. "I don't know how I made the putts."
But Ko knew what helped her. She was aided by caddy Brian Alexander, a longtime member of the Vancouver Golf Club. He has never caddied before and linked up with Ko by the luck of the draw after signing up with the tournament's caddy service.
While many pros travel with their own caddies, Ko has to get them wherever she goes. She said it has been a challenge finding good luggers, but she has lucked out.
"Two weeks ago at the U.S. Amateur, my mom caddied, and that is kind of a different feeling, because she's your mom and you have to listen to her," said Ko. "It was really comfortable having my mom there, but it's also really relieving and comfortable to have some that knows the course off their hat, really.
"He's been here for, I think 10 years, so he knows where not to go and where to go. There were quite a few tricky greens."
Alexander, a real estate developer, said he gave Ko tips on the course during practice rounds earlier in the week. However, she has been calling the shots since play began for real.
Four golfers — South Koreans Inbee Park and Na Yeon Choi and Americans Moira Dunn and Angela Stanford — were all tied for third at 5-under under 139.
Three other golfers, including 2009 champion Suzann Pettersen shared seventh place at 4-under 140.
"Well, this a round that has a little bit of everything," said Pettersen after firing a 3-under 69.
Her round included six birdies and three bogeys. She hoped to have a better read on the speed of the greens as she headed into the weekend.
So how does it feel chasing a 15-year-old?
"It feels like you're being beaten by a kid," said Pettersen. "I know she's good. The problem is, she's too young to understand where she's at."
First-round leader and world No. 1 Yani Tseng struggled in with a 3-over 75 — nine shots more than the day before — and found herself tied for 10th.
Tseng's putter let her down as she missed several birdie opportunities while only bogeying two holes. She doubled the par-3 second and had a single-bogey on the par-5 10th.
"I still have two days to go and, hopefully, next two days, I can fight back a little bit," said Tseng.