By Agence France-Presse
Thidapa or "Junior" thrust herself into title contention with an eagle-birdie finish at Highland Meadows Golf Club in Sylvania, carding a final-round 65 for a 14-under par total of 270.
She could only wait and watch for more than an hour as Lincicome and overnight leader Brooke Henderson of Canada tussled for the lead, Lincicome closing with a four-under par 67 for 270 as Henderson settled for a 69 that left her in third place on 271.
"Pretty much I just chilled out," Thidapa said of the wait, after which she just told herself, "I just had to do it and make the win."
The 25-year-old, who chipped in for eagle at the par-five 17th then birdied the par-five 18th in regulation, put her tee shot at the first playoff hole -- the 18th -- in the fairway as Lincicome found a fairway bunker.
Lincicome then blasted into the water hazard, as Thidapa put her third shot five feet from the pin.
Lincicome kept the pressure on as best she could, rolling in a six-foot putt to save par, but Thidapa calmly made her birdie putt for a long-awaited first victory.
"I never expected it was going to be today at all," said Thidapa, a Ladies European Tour winner who had only two prior top-10 finishes on the LPGA Tour.
"I've been struggling the whole year, trying to keep my tour card, trying my best. And finally all my work I've been doing has come out and shown today," added Thidapa, who joined sisters Ariya and Moriya Jutanugarn as the only Thai players to win on the LPGA Tour.
With the win, Thidapa earned one of five places on offer this week in the Women's British Open.
Lincicome, who started the day one shot behind Henderson, was tied for the lead at 14-under after her fourth birdie of the day at the 12th, where she rolled in a long, swinging putt.
Lincicome poised for PGA start
Henderson regained the solo lead with a birdie at 14 that moved her to 15-under, but the Canadian bogeyed 15 and 16 to fall one shot off the pace -- the first time since Friday she hadn't held or shared the lead.
With Thidapa in the clubhouse on 14-under, neither Lincicome nor Henderson could take advantage of the par-five 17th and 18th -- Lincicome's attempt to win it with a birdie at the 72nd hole circling inside the rim of the cup and popping out.
Lincicome will have little time to fret over the near-miss. On Thursday, she's due to tee it up at the Barbasol Championship, where she'll join the select group of women to play in a US PGA Tour event.
Swedish superstar Annika Sorenstam became the first woman in 58 years to appear in a PGA Tour tournament when she played the Colonial in 2003, missing the halfway cut.
Michelle Wie later competed in a handful of PGA events, never making the cut. Other women to play in PGA Tour events were Babe Zaharias and Suzy Whaley.