The 30-year-old from Nairn sits alongside Dane Anne Van Dam and Germany’s Leonie Harm after carding a six-under-par 66 at the Centurion Club near St Albans.
“I’m really chuffed with that,” said MacDonald of her bogey-free effort. “It has been a long time coming.
“My game has been there for a while. I just haven’t been able to maybe put it together in one round.
“I’m just delighted to get off to a good start – and the team is doing well, so I’m really happy.”
Her team sits in joint-10th on 11-under, five shots behind South African Lee-Anne Pace’s line up.
“I took a little bit more time on the greens today as I felt like that was really necessary and I holed a good few putts,” added MacDonald.
“I got off to a great start, hit rescue into nine feet at the first and made eagle, so that was just a huge boost.
“But I think the course does suit me just purely on the length. “It’s playing soft and I’m probably one of the longer hitters, so that’s a huge advantage.”
Two birdies on the 18th put Team Pace in pole position as they hold a one-shot lead.
Anne-Lise Caudal holed out on the last, while amateur James Carson Heard also made a birdie to put their team at the top of the scoreboard.
“It was really good. It is so great to play in this format. You just kind of go for everything and go for the birdies,” said Pace.