Australia's Hannah Green launched her LPGA Portland Classic title defense with a six-under par 66, sharing the first-round lead with American Cydney Clanton.
Green had seven birdies before her lone bogey of the day at the 18th, in fading light at Columbia Edgewater, where thunderstorms halted play for an hour and a half.
The tournament has been reduced to 54 holes because of poor air quality due to wildfires.
While Green was able to complete her round, more than a dozen other players were on the course when darkness fell, and will return to complete the first round on Saturday morning.
"I missed quite a lot of greens compared to my score, so the only putt I really missed was the one on the last, so to say that is pretty good,” Green said.
"I'm super-happy that we finished and super-happy with my round."
The 23-year-old Australian equaled the tournament's 72-hole scoring record with a 21-under winning total last year.
That was part of a breakout 2019 campaign that included a major victory in the Women's PGA Championship.
On Friday, she birdied four of the first five holes and after the weather delay returned with a birdie at the par-five seventh.
She picked up strokes at the par-three 13th and the 17th to take sole possession of the lead before her birdie at the last.
That put her level with Clanton, who teed off early and shook off an early bogey at the fourth.
The American's seven birdies included five in the last eight holes.
"I finally made some putts," Clanton said. "It's also nice to hit some really close and had a par-five in two have a two-putt. So, it was really nice to see the ball starting to go in the hole."
Germany's Caroline Masson, Mexico's Gaby Lopez, England's Mel Reid and American Amy Olson were in the clubhouse on five-under 67.
Yealimi Noh was five-under with one hole left to play when darkness halted play.
South Korea's Lee-Mi-rim, coming off her first major victory at the ANA Inspiration on Sunday, carded a 70.
Lee defeated American Nelly Korda and Canada's Brooke Henderson in a playoff at Mission Hills. Both Korda and Henderson -- who won the Portland title in 2015 and 2016 -- withdrew this week because of the air quality concerns.