Brittany Lincicome is in danger of missing the cut at the PGA Tour's Barbasol Championship where she is competing against male rivals.
The 32-year-old two-time major champion, who is playing on a sponsor's exemption, is only the sixth woman to start a PGA event.
But she had two bogeys, a double-bogey and triple-bogey and just one birdie in her six-over round of 78.
"I enjoyed my time out there, but it was pretty nerve-wracking," she said.
Most of the world's top male players are in action at the Open at Carnoustie this week.
Michelle Wie, Annika Sorenstam, Suzy Whaley, Shirley Spork and Babe Didrikson Zaharias are the only other women to have competed alongside the men in the PGA's 102 years.
Lincicome, who began on the back nine, had two bogeys and a double-bogey in her opening nine holes.
The highlight of her round was sinking a 30-foot birdie putt at the par-four third.
"I was just hoping it got somewhere near the hole," she said. "When it went in I was like, 'Oh my gosh, finally got my first birdie.'
"I was hoping there was going to be a train of more of them, but maybe they're coming tomorrow.
"Hanging out with the PGA Tour guys inside the ropes, there's no cooler feeling in the world. The guys were really great, they were welcoming. Their short games are incredible."