The duo dropped only one shot and finished with six straight pars for a four-under 66 and a one-shot lead over six teams, including Lexi Thompson and Meghan Kang, and Leona Maguire and Jennifer Kupcho.

Defending champions Ruoning Yin and Jeeno Thitikul, both among the top five in the women's world rankings, are among those two shots behind at 68 in the LPGA Tour's only team event.

Dryburgh is a 32-year-old from Scotland, while the 22-year-old Porter is enjoying her rookie season on the LPGA Tour. They carefully picked out which holes for the longer Porter to start at Midland Country on Thursday.

"Cassie hits it further than me, and I'm nice and down the middle usually," Dryburgh said.

"We kind of picked the right holes for each other, and I think we gelled really well. We complemented each other really nicely."

Thompson, who has gone six years without an LPGA victory, and Khang had five birdies offset by two bogeys. 

"I knew coming out here for alternate shot that we just had to make a few birdies and pars were good," Thompson said. "Just tried to stay consistent and be patient."

Maguire and Kupcho had an early bogey and then played bogey-free with four birdies over the final 16 holes to join the large group at 67.

For an alternate-shot format that can be stressful, Maguire and Kupcho kept it simple. Both are rarely out of position and consistently good putters.

"We don't get too aggressive on attacking pins," Kupcho said. "So we give ourselves lots of putts and kind of have our speed under control and kind of just make it easy on each other."

Kupcho teamed with Lizette Salas to win the 2022 event.

Australian Karis Davidson and Daniela Darquea (Ecuador) are tied eighth at two under.

Robyn Choi, the only other Australian in the field, is tied 20th with American Jenny Bae after finishing with par.   

The format switches to fourballs on Friday, which yields lower taking the lowest score of each player.