Taiwan's Tseng is a two time winner here, having won in 2011 and 2012. She is a five times major winner.
She could have had the lead outright, but dropped a shot on the final hole, however her round included seven birdies and a bogey.
Tseng said: "Could be better, could be worse. I miss(ed) couple short putts, but I just tell myself to smile and let it go."
Local favourite Ariya Jutanugarnwas one of six players just one shot behind on 67; with four more players within two shots of the leaders.
The American duo of Lewis and Lang share the lead after a good start for Lewis and a poor start but a great comeback at the end of the day from Lang.
Lang said: "I got off to a good start with a birdie on 10 and 11. I was just really seeing my shots and committing to them. Just felt effortless really."