"It's just crazy in my mind right now," Thitikul said.

"I cannot believe that I became LPGA winner. It feels amazing as well."

After Koerstz Madsen's 15-foot bogey putt hit the edge of the cup and stayed out, Thitikul rolled her 10-foot par try close and holed out for the breakthrough victory.

"A lot things going through my head," Thitikul said.

"But one thing that I really want to focus is like just, 'Do your every single shot.' Just like, 'If you lose, if you win, this is another chance to learn. So do your best every single shot'.

"I cannot believe that I became LPGA winner. It feels amazing as well." - Atthaya Thitikul.

"That's it."

At 19 years and 25 days, Thitikul is the youngest winner on the LPGA Tour since Brooke Henderson in the 2016 Portland Classic at 18 years, 9 months, 23 days.

The Thai player also has two victories on the Ladies European Tour.

Koerstz Madsen lost two weeks after winning a play-off in Thailand to become the first Danish champion in LPGA Tour history.

They matched pars on the first extra trip down 18, with Thitikul missing an eight-foot birdie try.

Koerstz Madsen drove left on the second playoff hole and hit her second from an awkward stance near the cart part into the greenside water.

Thitikul shot an eight-under 64, making nine birdies and a bogey to post at 16-under 272 at Aviara Golf Club in the final event before the first major of the season next week at Mission Hills in Rancho Mirage.

Koerstz Madsen, three strokes ahead of Na Rin An and six clear of Thitikul entering the round, had a 70.

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An was third at 15-under after a 68.

Top-ranked Jin Young Ko (68) was 14-under in a three-way share of fourth with Pajaree Anannarukarn (68) and Maude-Aimee Leblanc (68).

Coming off a victory three weeks ago in Singapore, Ko extended her Tour record for consecutive sub-par rounds to 34.

She's won six of her last 11 tournaments.

"I'm very excited to play next week's major," Ko said.

"But this is a little sad, too, last tournament at Mission Hills."

Minjee Lee (71) headed the Australian contingent but was a distant nine shots off the pace at seven-under while her fellow major champion Hannah Green (70, two-under), Katherine Kirk (72, even) and rookie Steph Kyriacou (78, three-over) were further back.