Lang, who tied for second at the 2009 Yokohama Tire LPGA Classic, birdied five of her first seven holes before ending the day two ahead of fellow Americans Ryann O’Toole, Tiffany Joh and Sydnee Michaels.
American world number three Stacy Lewis, tournament champion in 2012 and a runner-up last year, launched her bid for a first LPGA victory in 14 months with an opening 70.
“It was just one of those days, it was so enjoyable,” Lang told reporters after soaring to the top of the leaderboard with nine birdies and two bogeys.
“I wasn’t thinking about a whole lot. I was just super committed to seeing my shots, it was so much fun.”
“I played pretty flawless golf. Even when I was making pars, I was burning the edge from 10 feet. Every hole I was right there.”
Lang was delighted that she rebounded from her only bogeys of the day, at the 13th and 14th, with consecutive birdies from the 16th.
“The birdies on 16 and 17 were pretty big after the bogeys … not stupid bogeys, small misses, but I stayed aggressive so I was excited with that,” she said.
“I had one of my better years I’ve ever had and the Solheim pick’s over with. I’m just in a really comfortable place, so I just felt really relaxed out there.”
Lang has triumphed only once on the LPGA Tour, at the 2012 Manulife Financial LPGA Classic where she edged out South Koreans Chella Choi, Park In-bee and Seo Hee-kyung in a four-way playoff.
South Korean Hur Mi-jung, who set a tournament record with a 21-under winning total last year, launched her title defence with a two-over 74.
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Greg Stutchbury)