Henderson made a long birdie putt on her final hole, the par-3 ninth, for a 29 on the front nine to move past a group that included Jin Young Ko and Patty Tavatanakit on Thursday.
"Up until this year, ball-striking has definitely been a strength of mine, and hasn't been as sharp as I would like the last couple months," said Henderson, who switched irons recently and felt she was headed in the right direction.
"To hit all 18 greens is more what I used to be used to a little while ago.
"It feels amazing not to have to get up and down and give myself a lot of birdie opportunities."
Henderson won the season opener in Florida and hasn't won since, falling to No.13 in the women's world ranking and coming in at No.14 in the Race to CME Globe.
This is the last tournament for the top 60 players to reach the season-ending CME Group Tour Championship down the coast in Naples.
That's not an issue for Henderson or Ko, who is No.5 on the strength of two LPGA victories this year.
It's a different story for the others who were at 63. Tavatanakit, a former major champion, is at No.61 and got off to the ideal start.
"I've been like preparing for this event. Obviously, I knew what I had to do," Tavatanakit said.
"I'm pretty stressed, but at the same time, I feel like I did everything under my control.
"I did everything with no regrets. I'm just going to be out here and know at the back of my mind that I did everything I could."
Emily Kristine Pedersen is at No.80 and Japan's Minami Katsu is at No.78. They also were at 63.
Katsu rallied late on a beautiful day at Pelican Golf Club, starting the back nine with five birdies in six holes to get near the top of the leaderboard.
Lexi Thompson, playing for the first time since missing the cut by three shots in Las Vegas on the PGA Tour, opened with a 64 to be in a five-way tie for sixth.
She has gone more than four years without winning and will likely need to finish third or better to make it to the season finale in Naples.
Defending champion Nelly Korda opened with a 70.
Lydia Ko had to settle for a 67 and at No.101 in the Race to CME Globe, she likely would have to be alone in second to reach the Tour Championship and defend her title.
Sarah Kemp (68), who is tied 46th, is the best of the Australians ahead of Gabriela Ruffels (69), Stephanie Kyriacou (70), Grace Kim (71) and Su Oh (72).
Major winners Minjee Lee and Hannah Green are not playing.
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