Shanshan Feng set a high target for such low scoring at the LPGA Tour event in Wisconsin that she figured she had done enough.
Three birdies in a four-hole stretch had taken her from three shots behind to a one shot lead on Sunday, or so she thought.
It was only after she hit seven-iron to three feet on the final hole that she saw the leaderboard and realised she was tied with Ariya Jutanugarn.
"I'm like, 'Oh, no. I have to make that one'," Feng said.
Leaving the flagstick in, she rolled in her final birdie putt for a nine-under 63 and a one-shot victory over Jutanugarn, who had hit eight iron to three feet for birdie and a 64.
Feng won for the 10th time on the LPGA Tour but it was her first victory since November 2017.
Her score of 29-under 259 was two shots shy of the LPGA record that Sei Young Kim set last year on the same course.
The shootout on the soft Thornberry Creek at Oneida course materialised the way everyone expected.
Patty Tavatanakit shot 61 and was part of a five-way tie for the lead before the final two groups even teed off. She wound up in a tie for 15th.
Seven players had at least a share of the lead at some point in the final round.
Jutanugarn, a former world No.1 still searching for her first victory this year, appeared to be in control with a three-shot lead on the back nine.
She holed a bunker shot for an eagle on the reachable par-four sixth. She closed out her 30 on the front nine with another eagle.
But the Thai pulled her tee shot on the par-five 15th, turning a birdie hole into a bogey that cost her momentum and the lead.
In the group behind her, Feng ran off birdies at the 13th, 14th and 16th holes, the last one a dart into two feet that gave her a one-shot lead.
Jutanugarn wasn't finished, however, with her final full shot covering the flag and setting up birdie.
Feng had the last word.
"Before the round today, I didn't know what the others were going to do, so I was aiming for 30 under," Feng said.
She finished just a shot shy of that.
It was the second close call in three weeks for Jutanugarn, who played in the final group at the Women's PGA Championship at Hazeltine and failed to make a birdie as Australian Hannah Green won.
"Overall, my whole week was really good," Jutanugarn said.
"It's like amazing, because I didn't expect to play that good at all, so I'm really happy about how I played."
Tiffany Joh birdied her last three holes for a 67 and tied for third with Amy Yang (65) at 25 under.
Impressive teenage qualifier Yealimi Noh finished tied sixth at 23 under after a closing 68 to sit alongside world No.1 Sung Hyun Park (69).
"It was my goal to be in the top 10 for the week," the 17-year-old Noh said.