Korda won six times in seven starts on the LPGA Tour between January and May, including her second major at the Chevron Championship.
However, she failed to even make the cut at two of the last three majors since.
A bogey-free round of 68 took the American three strokes clear of defending champion Lilia Vu and Britain's Charley Hull. The trio played together in a star-studded group on the opening two days.
Korda credited a change of putter for a turnaround in her form from the last couple of months.
"I just needed something different to look at. Sometimes you just need to switch it up," she said after battling heavy wind and rain on Scotland's east coast.
"I'm just trying to stay very present and not think about anything other than one shot at a time, and whatever golf and links golf throws at me, I'm going to take it head on.
"I think when the conditions are a little tougher, in a sense, normal golf is thrown out the window and you're just trying to play the wind."
World number two Vu was two under for the day to ease into contention.
Hull had topped the leaderboard on Thursday, but missed the chance to move into pole position for her first major after an even par round left her three shots back.
"I actually I thought I hit it just as good as yesterday," said Hull.
"I just missed three or four four-foot putts, but that was early on in my round.
"But then, once I got over that, I just fell back into my stroke and it felt fine.
Olympic gold medallist Lydia Ko is also among 10 players within five shots of the lead at three under par.
