Lydia Ko signaled she is ready to collect her second Evian Championship after a bogey-free 66 in the first round of the fourth major of the women's season on Thursday.

The New Zealander became the youngest winner of a women's major when she lifted the Evian trophy as an 18-year-old in 2015 and a flawless round on the opening day put her in joint second place and two shots behind the leader, Paula Reto.

South African Reto was the surprise front runner on seven under par 64 after a bogey at her second hole was followed by a haul of eight birdies.

Ko shared second place on five under with American Alison Lee, Thailand's Wichanee Meechai and Celine Boutier, who is hoping to become the first home winner.

"It certainly wasn't easy today," admitted 26-year-old Ko, currently ranked three in the world.

"I was scrambling to make pars on the front nine, but I was good at getting out of trouble.

"Sometime par saves are the momentum to start making some birdies and it was nice to make a few on the back nine and finish off with one at the last. Played so well coming home and, hopefully, it will not be such a shaky start tomorrow."

She added: "I changed my putter at the US Women's Open and it's been really good so far. I'm rolling it well and I'm so looking forward to the rest of this week."

Ko, whose second major win came in the 2016 ANA Inspiration, had only 24 putts in pursuit of a third major and was the only player in the afternoon draw to make a significant move.