The 19-year-old New Zealander said a video he showed her of her first career hole-in-one at the Olympics in Rio sparked her 10-under-par round on Friday at Tiburon Golf Club.
“Brings back a lot of great memories," said world number one Ko, the Olympic silver medallist who has gone without a victory in her last nine events. "It was something I couldn't ever have dreamed of.
“To see that swing, you know, I was hitting the ball really well at the Olympics. It gave me all the positive thoughts."
Ko posted 11 birdies, starting the round with three in a row and registering seven on the back nine against a lone bogey, taking just 22 putts to reach 12-under-par 132.
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Sharing second on nine-under were South Korean Ryu So-yeon (67) and American Ryann O'Toole (68).
Feng, winner of her last two events, struggled to a one-over 73 to stand tied for 16th at five-under.
A win at Tiburon would give Ko her third successive $1 million bonus for winning the Race to the CME Globe points chase, and would clinch Player of the Year honours over Thai Ariya Jutanugarn.
Jutanugarn, a five-time winner this season, shot 68 on Friday after an opening 72 to stand four-under.
(Writing by Larry Fine in New York; Editing by Peter Rutherford)
