Canadian Brooke Henderson leads LPGA San Francisco event

Canadian Brooke Henderson upstaged fellow teenager and birthday girl Lydia Ko by firing a tournament record seven-under 65 to take a two-shot lead at the Swinging Skirts LPGA Classic.

The 17-year-old Henderson, a long hitter who still needs sponsor exemptions to enter tournaments, reeled off six birdies and an eagle to vault to the top of the leaderboard at nine under par.

Despite playing only her 10th tournament, Henderson said she was prepared for a nailbiting weekend.

"I think I'm ready," she said. "Yeah, 17 is young. As you've seen with Lydia Ko and Lexi Thompson and even Jessica Korda, there are a lot of great names that have been able to do it. I'm hoping that I'm one of them."

South Korean Choi Na-yeon was alone in second place at seven-under while Japan's Sakura Yokomine and China's Yueer Cindy Feng were joint third three shots back at six-under at the Lake Merced Golf Course in San Francisco.

World No 1 and defending champion Ko was serenaded by the galleries on her 18th birthday but her game was off-key during a level-par 72 which left her at five-under.

"I really didn't get anything going," said the New Zealander. "When that happens it's really hard.

"You know, I would say the par-fives, you kind of need to take advantage of them. I didn't position myself well in any of them, and that just makes it tough. Kind of feel like you're already losing shots there."

American Stacy Lewis shot a one-under-par 71 to sit five strokes off the pace at four-under.

Juli Inkster was the story of the opening round after the 54-year-old finished one shot out of the lead, but her second round 74 dropped her to two over par.

Michelle Wie endured her second consecutive over-par round, scraping out a 74 that had her five-over for the tournament and just above the cut line.