Choi Hye-jin fired a five-under par 66 to match South Korean compatriot An Na-rin for the lead after Saturday's third round of the LPGA Canadian Women's Open.
The LPGA rookies, standouts on the Korean tour each chasing her first LPGA crown, shared the top spot on 16-under 197 after 54 holes at Ottawa Hunt and Golf Club.
South African Paula Reto, chasing her first LPGA victory as well, was on 198 with Americans Nelly Korda and Sarah Schmelzel sharing fourth on 201.
An held a two-stroke lead after Saturday morning's completion of the rain-interrupted second round and stretched her advantage with an early run that saw her birdie the par-4 second, the par-3 fifth and par-5 sixth.
But An followed a birdie at 12 with a bogey at 13 to stand on 16-under, while Reto and Choi each made a birdie at the par-3 15th to pull within one stroke.
Choi birdied the 16th, her fifth birdie in eight holes, to match An for the lead and they stayed deadlocked to the finish.
"I started off with a bogey but I was able to play really well after that," Choi said through a translator. "At the end of the day, you want to be competitive."
An, 26, had a season-best finish of third at Carlsbad in March. She shot 68 on Saturday.
"I didn't feel like I was as good as I was yesterday but I still hit the shots I wanted," she said through a translator. "I was very lucky today."
Choi, the 2017 US Women's Open runner-up, has been in the hunt for her first LPGA title this year at majors, taking third at this year's US Women's Open and sharing fifth at the Women's PGA Championship.
"I've been close so many times it would be an honor if I could win," Choi said.
"I'm going to be thankful no matter what," An said.
Reto, who fired a course-record 62 on Thursday, shot 67 on Saturday and hopes to follow on after taking her first pro title in February at South Africa.
"I'm able to be more consistent on the golf course," Reto said of her improvement. "It's nice to see the shots and be able to pull them off."
Korda, the Tokyo Olympic champion, won a Ladies European Tour title last week in Spain and could become world number one with a victory Sunday.
"It felt really nice to get the win in Spain, reassure myself I could win and give myself good momentum coming in here," Korda said.
"You can be pretty aggressive coming into the greens. You aren't going to move up unless you make the putts. Hopefully I can get a good run tomorrow."