Stephanie Meadow heads the trio of Irish challengers on two under, just four shots off the leader, Nelly Korda, at the ANA Inspiration tournament in California, the year's second major.
The Jordanstown native was among the late starters, sits in a share for 19th place, making steady progress initially with birdies on the fourth, sixth and 11th which got her within a shot of the lead on three under after 12 holes.
But consecutive bogeys on the 13th and 14th holes saw her slip back to one under.
However, a birdie on the par five final hole leaves her on two under and within striking distance heading into round two after that opening 70.
Leona Maguire was three shots further back as the Cavan golfer carded a one over par 73 at the Mission Hills Country Club. She birdied the third, 11th and 18th but bogeys on eight, 13, 14 and 16 saw Maguire drop a shot.
Olivia Mehaffey was also among those to take to the course early. The amateur player, based at Arizona State University is four shots behind Maguire on five over after shooting a 77.
The Tandragee, County Down native managed three birdies but carded eight bogeys in the first round.
Leader Korda pushed through the heat on the first day in California to hold a one-shot lead after carding a six-under 66.
The American had birdies on the first and third holes before carding another five birdies and nine pars at the Mission Hills Country Club at Rancho Mirage.
The 22-year-old said managing the heat, which reached 34 degrees in the middle of the day, was crucial.
"It was definitely hot at the start of my round, then towards the end of it we got a little bit of cloud coverage, so that was really nice. And just drinking lots of water and staying really patient out there is key," she told reporters.
South Korean In Gee Chun and Sweden's Madelene Sagstrom both carded a five-under 67, while world No 2 Danielle Kang is among five players sitting tied for fourth.
England's Mel Reid and Georgia Hall are three strokes back from the lead with a share of ninth.
Prior to the tournament's start, controversy over the omission of new major champion Sophia Popov gave way to concerns over the extreme heat.
Caddies have already been told they can use carts for tournament rounds and that could be extended to players with the situation being exacerbated by smoke from California's wildfires
