Leona Maguire also made strides with a 67.
Overnight, the pair sat in tied 36th and tied 22nd place and were determined to make a move towards the medal positions.
At the end of play on Thursday, they had both moved into a tie for 11th.
Nelly Korda (USA) fired a superb round of 62 which gives her a 4-shot advantage over Aditi Ashok (India), Nicole Koerstz-Madsen (Denmark) and Emily Kristine Pedersen (Denmark) who are tied for the silver medal on 9-under.
Already with five birdies on her card before reaching her final hole of the day, Maguire signed for her 4-under par round by finishing off with an additional birdie. She credited her opportunity creation for her score, something she struggled with on day one.
“I played a lot better today and gave myself a lot more chances,” said the Cavan native. “I didn’t get off to the best of starts but I chipped in on 4 and I kind of feel like that turned the day for me.
“I then went on and had three birdies in a row on 6, 7 and 8 which was nice. It felt like I played quite solid today.
“There were a few putts that, had they gone in, it would have completely changed the day, but it was nice to finish with a birdie on 18 to head into tomorrow.”
Upon finishing her round, Maguire was also delighted to hear of boxer Kellie Harrington securing her place in the gold medal fight to take place this Sunday.
“What Kellie is doing is incredible,” Maguire said.
“She was one of the first people I met when I got into the village last week. I’d love to see her win a gold medal, she really deserves it. It’s great to see the community and people at home rallying around her. I’m fortunate where I’m from it’s the same as well.
“If we can finish off this week on a high note and she can go win a gold medal on Sunday, that would be great.”