Lewis has a one-stroke lead over Michelle Wie (-2), while a handful of other players are at one-under.
Meanwhile, on the PGA Tour, Manawatu's Tim Wilkinson has made a useful start to the Travelers Championship in Connecticut with a four-under 66, leaving him a tie for 16th after the opening round.
Wilkinson made four birdies during his bogey-free round and is four shots back from leader Brendan Steele who carded an impressive eight-under 62 today.
Kiwi Danny Lee will need to improve during his second round after he fired a disappointing two-over 72 to be in a share of 120th.
On the second-tier Web.com Tour, Hamilton's Steven Alker opened with a two-under 68 to sit in a share of 34th at the Air Capital Classic in Kansas.
Alker, who missed the cut at last week's US Open, is five strokes back from leader Aaron Watkins who began with a seven-under 63.