Ko carded a bogey-free three under par to be in a tie for eighth, five shots behind the leader, South Korea's Sung Hyun Park.
Park hit eight of 13 fairways and all but one green in regulation.
Aditi Ashok birdied three of four par-5s, but also dropped three bogeys and a double bogey to finish with a modest one-over 72 in the opening round of Evian Championships, the season's fifth and final golf Major for women, on Friday. Now, she's four behind her.
Seizing a second chance to play the first round at the Evian Championship, Park fired an eight-under 63 to lead by two shots from Moriya Jutanugarn of Thailand.
That meant a 14-shot turnaround in fortunes for the No. 3-ranked South Korean.
The former world No.1 enjoyed the cool conditions which were a far cry from the driving wind and rain which forced organisers to abandon the first day and reduce the tournament to 54 holes. But on Friday, the reigning U.S. Women's Open champ took full advantage of the do-over, firing an opening 63.
"The distance was 25 meters, so I was deciding whether I'm going to do chipping or putting, and I think after I made the shot, I was surprised, as well", Park said about her eagle. Jessica Korda and In-Kyung Kim was at four-under par. Jessica Korda of the United States and Women's British Open victor In-Kyung Kim were a further shot back on 4 under.Park played in a stellar group with top-ranked So Yeon Ryu (75), her fellow South Korean, and No. 2 Lexi Thompson (70) of the U.S.Ryu suffered a six-shot swing having been 2 under and sharing the lead with Korda on Thursday when play stopped.
Ryu suffered a six-shot swing having been two-under and sharing the lead with Korda on Thursday when play stopped.
Forecast weather is for "pretty good" playing conditions for the next two days and some more rain Sunday, Whan said, noting that 45 miles per hour (72 kph) gusts were experienced Thursday.
World number one Ryu So-yeon, who had made a promising start on Thursday, endured only frustration.