Just behind them at 4-under par 68 are Brittany Linciome, Suzann Pettersen, Jennifer Johnson, and Jiyai Shin. Sun Young Yoo, Amy Yang, and Stephanie Sherlock are all at 69.

Tseng is picking up where she left off at the RR Donnelley Founders Cup last week when she scored her second victory of the season.

Her round at Carlsbad was marred by only a single bogey, at the eighth hole, her 17th of the day.

“Today I was just really patient because I don't hit lots of fairways,” she said. “ I think I only hit six fairways today. This golf course is very narrow, and the rough is really long. If you don't hit on the fairways, it's kind of very hard to get close to the pin.”

Oh, a six-year LPGA veteran at age 23, is looking for her third LPGA win. She birdied four of her last seven holes to gain a share of the lead.

Hedwall, who played a key role in Europe’s Solheim Cup win last summer, played in one of the last groups of the day. She went out in 4-under par 32, then recorded a pair of bogeys at 10 and 13. She got back in gear however with birdies at 14, 15, and 16.

A total of 25 players broke par. Defending champion Sandra Gal carded an even-par 72.