Playing against the pros for the first time in her career, Duncan had the home fans roaring as she started her final round with a birdie before going on to close with a level-par 72 for a seven-under 281 total.
The sensational effort earned the Women’s Amateur champion a tie for tenth, becoming the first Scot since Monifieth’s Kathryn Imrie in 1988 to claim the Smyth Salver as leading amateur and the first to do so since it became a major.
“I feel a bit mind-blown, as if it’s not happened yet,” admitted Duncan. “It will maybe take a couple of weeks to sink in. I feel over the moon about how I played and handled it. I had a great time and I am really happy how I played over the four days.
“I don’t know what the expectation was, but it has definitely been exceeded. I couldn’t have written the week any better. I’m glad it’s not a fluke and I played well all four days.”
Duncan, who started the day just two shots off the lead after delighting the home fans with a stirring Saturday effort in the rain, received a huge cheer as she appeared on the first tee ahead of her 2.25pm tee time.
Playing alongside Swede Madalene Sagstrom in the third last group, the Scot calmed any nerves she may have had by safely finding the fairway with an iron then raising an even bigger roar than the earlier one as she calmly rolled in an eight-footer for an opening birdie.
It was the third time in four rounds that she’d got off to the perfect start and there was no disguising the excitement among the huge throng of fans following the home player as she marched confidently to the second tee.
With Scottish Amateur champion Angus Carrick and Scottish Women’s Amateur runner-up Tara Macataggart among those watching on, Duncan split the fairway with her drive at the second and wasn’t far away from making it a birdie-birdie start from around 15 feet.
Most players were taking an iron to lay up short of the two fairway bunkers at the third, but not Duncan. Oozing with confidence, she flew the trouble to leave herself with just a wedge. A bit heavy-handed with that, her putting touch was exquisite as a par-4 went down on the card.
That was repeated at the next, where a testing three-footer was confidently converted, before a 10-foot birdie chance went abegging at the fifth after she’d taken dead aim at the flag on the back tier.
Duncan’s average driving distance heading into the final round had been 283 yards, bettered only by Lexi Thompson, while the Scot was tied for 22nd for fairways hit with an average of 67 per cent.
On the back of those statistics, she would have been disappointed that she had to settle for a par at the long sixth - eight of the players in the final five groups made birdie there - from the middle of the fairway.
Duncan then dropped her first shot of the day after being left off the tee at the ninth then right behind a bunker with her approach, but, not for the first time during the week, the Ayrshirewoman showed she’s made of stern stuff.
Only the second player to achieve the feat in the final round, she made a brilliant birdie from 15 feet at the 10th before making it back-to-back gains with a two-putt 3 at the next, where the tee had been moved up to make the green driveable.
Four straight pars were followed by a bogey-4 at the 16th before she then dropped a shot at the last, but the rapturous reception for her at the end said it all. Scottish golf has a new star.
“It was a great start with the birdie as I wasn’t expecting that,” she said. “I left a few shots out there, to be honest. I felt I was rolling my putts pretty well, it was just unfortunate that not many went in.”