Pettersen has won two of her last three starts and birdied two of the final three holes in Naples, Florida, to match the South Korean pair Sun Young Yoo and So Yeon Ryu on a six-under 66.
LPGA rookie of the year Ryu joined Norway's Pettersen in clawing back to parity with Yoo, who bogeyed and double bogeyed towards the end to lose three shots from nine under.
"I still feel like I have the best golf ahead of me," Pettersen said. "I'm not too worried if it's season 2012 or season 2013.
"My big goal now is to prepare and be well for 2013 and hopefully come out strong the way I finish, and hopefully get another three rounds together and see where that takes me for this tournament."
Yoo said: "I hit the ball great all day, but I'm a little disappointed how I finished the last couple of holes.
"But still, 6 under was a good score. ... I still have 54 holes to play, so I feel good."
Stacy Lewis, LPGA player of the year, needs success at TwinEagles to have any chance of securing the money title but also succumbed to two over-par holes late on, forcing her to settle for a first-round 70.
- Sports & Recreation