Megan Khang has birdied four of the last five holes for a four-under 68 and a three-stroke lead in the CPKC Women's Open.
Australia's Hannah Green dropped to seventh with an even-par 72 taking her to three under after 54 holes, while Gabrielle Ruffels (71) is two shots further back in a tie for 11th.
Seeking her first LPGA Tour victory, Khang rebounded from bogeys on holes 10 and 12 with birdies on 14-16 and 18, finishing by holing a 15-footer on the last.
"I'm just going to try my best to keep that same mindset, stay patient," Khang said.
"These fairways are tight and the greens are firm and (I need to) really trust myself out there."
The 25-year-old American had an 11-under 205 total at Shaughnessy Golf and Country Club in Vancouver.
While winless on the tour, she has 33 top-10 finishes, career earnings of more than $US5 million ($A7.8 million) and is ranked 27th in the world.
"It's a lot of learning over the past few years to stay patient, don't get too ahead of myself," Khang said.
Three strokes ahead at the turn on Saturday, Khang found herself two shots behind Sei Young Kim a few holes later before rallying with her birdie spree.
"I bogeyed 12 and then just like that I look at the leaderboard and I hear a roar," Khang said.
"Not knowing who it is I take a peek at the leaderboard and I see Sei Young's name up at the top and I'm like, 'Oh, here we go'."
Kim was second after a 67. The 30-year-old South Korean had a hole-in-one on the 175-yard eighth with a 5-iron and made an 18-foot eagle putt on the 265-yard, par-4 14th.
She won the last of her 12 tour titles in 2020.
Fellow South Korean player Jin Young Ko, who has 15 LPGA Tour victories under her belt, was third at six under after a 71.
"Today was long day," an exhausted Ko said. "The last three holes I didn't have energy."
Karis Davidson (70) is in a tie for 18th at even par, while two-time major winner Minjee Lee (69) is a short further back in joint 24th.