Kirk - who was looking for her first victory since the 2010 Navistar LPGA Classic - began the final day four shots ahead of Buhai and nine shots ahead of Kim, who threw down the gauntlet with a final round 63 which she finished 45 minutes ahead of Kirk and Buhai.
Kirk appeared to be wobbling with dropped shots at the 10th and 11th and, at that point, was tied with Buhai and Kim at 20-under, although Kim was four holes ahead and the pressure was on for Kirk and Buhai to respond.
Kirk did just that when she birdied the 12th and 13th holes to draw two clear but a bogey from the greenside bunker at the 17th would see her just one ahead as she walked to the 18th tee.
Both players hit solid tee shots at the last and Kirk was first to play her approach. She likely needed a par at worst to hold off Buhai, who was chasing her first LPGA Tour title.
Holding up under what must have been the most intense of pressure, Kirk hit her approach to 12 feet, throwing down the challenge to her playing partner who appeared then to need at least a birdie to force the issue.
Buhai, who has won twice on the Ladies European Tour but missed the cut in eight of her 12 starts on the LPGA Tour in 2017, displayed why she is considered a much better player than her results to date would suggest by hitting a brilliant approach to three feet.
Kirk would therefore need to convert the birdie opportunity she had so magnificently created and she did, extinguishing all challenges and taking the title by one over Buhai with Kim finishing one shot further back in 3rd position.
"So much hard work and patience,” said an emotional Kirk when asked by on-course commentator, Jerry Foltz, soon after her win to put into words what the victory meant to her.
Source: Twitter (@LPGA)
“I had a rough couple of years in 2015 and 2016 but having just an amazing team behind me – my husband has been 100 per cent supportive all the time so – I can’t put it into words, it is just a great feeling. It is an individual sport but it is certainly a team effort.
“I hit a really low spell around 14th and thought, gosh, I needed to something to happen her as I was just struggling but Ashleigh played great and put the pressure on all the way so full credit to her.”
Minjee Lee recovered from a very slow start to the week to finish 20th and the next best Australian behind Kirk while Karrie Webb was well back in 75th position.