World number one and Olympic champion Korda continued her brilliant recent form with a five-under-par 67 to share the lead with Sweden’s Madelene Sagstrom and South Korea’s Sei Young Kim.
But arguably the most impressive round of the day came from 21-year-old Stirling University student Duncan, who carded an eagle and four birdies to match the 68 of playing partner and 2018 winner Georgia Hall.
“It was a ridiculous amount of fun, I wasn’t expecting that at all,” Duncan, whose caddie and university coach Dean Robertson is a former European Tour player, told Sky Sports. “I’m over the moon with it.
“I was so nervous at the start. I was shaking and could barely put the ball on the tee. To actually make contact and it go straight was a bonus.
“The course is in great condition and it was actually quite playable. There’s good scores out there definitely and to finish off with four pars I’m extremely happy because it’s a tough stretch.
“It was really nice to have a few of my friends and family here, supporting me all the way round.”
Korda is now a combined 87 under par for her last 21 rounds, a run which includes her first major title in the Women’s PGA Championship and Olympic gold in Tokyo earlier this month.
“I’m very happy,” the 23-year-old American said. “It was very chilly in the morning, that was the only thing against us today but the wind kept calm and I took advantage of it.
“I’m a little tired but I’m still going to give it my all these next three days. I’ll go home next week, have one week at home and sleep in my own bed for the first time in six weeks which will be nice and then Solheim (Cup), we start up again.
“It’s going to be quick but I’m trying to take my recovery as seriously as possible.”
Asked if she enjoyed being the pre-tournament favourite and focus of attention, Korda added: “You strive to be in this position so it feels good but you kind of know that you have a target on your back.
“I just try to take the positives and see how it goes.”
Sagstrom looked set to hold the outright lead when she posted her seventh birdie of the day on the 15th to move to six under, but bogeyed the 18th after an errant drive.
However, the 28-year-old will have impressed playing partner and Solheim Cup captain Catriona Matthew who will name her six wild cards on Monday after the six automatic qualifiers are decided on Sunday evening.
“Of course I want to show off my game to her. I can’t deny that,” Sagstrom said. “Who knows where her mind is at right now? I’m just trying to play as well as I can to give myself a chance for that team.
“I haven’t put too much pressure on myself this time. I put a little bit more pressure on myself both in ’17 and ’19, really wanting to make that team, and I’m kind of at a state where I’m like, if I’m good enough, I will make that team.”
England’s Charley Hull is set to qualify for the Solheim Cup side but started with a double bogey on the first and made another on the 17th in her 77, while Matthew was a shot worse off following a birdie-free 78.
Defending champion Sophia Popov carded a level-par 72.