The 17-year-old stood by the side of the final green in tears as she watched South Korean world number four Inbee Park lift the trophy and the $225,000 cheque after throwing away a two-shot lead on the 72nd hole in a stunning collapse on the Pattaya Old Course.
Having led overnight by three shots, Ariya, playing on a sponsors invite, showed few signs of nerves as she battled the game's elite, including world number one Yani Tseng, on a pressure-filled Sunday in Thailand.
Standing on the 12th tee, she fired her approach to the par three and gasped with joy as the ball had just enough pace to trickle into the cup and take her back in front on 14 under for the tournament.
Ariya extended her advantage with a birdie at the 13th but dropped a shot on the next hole before regaining her composure with three straight pars to leave her two ahead standing on the par-five 18th.
But just as she was set to become the first Thai to win an LPGA event everything unravelled on the last. Her misery complete after she failed to force a playoff when her four-foot putt lipped out handing a stunned Park victory.
"I didn't expect this result either, I had a great round today but thought it wasn't enough. I don't know what to say, I'm still very shocked," Park said in a televised interview after her five-under 67 gave her a one-shot win.
"After she hit her fourth shot I thought I had a chance of a play-off. I was ready, but it became even better.
"She played incredible golf the last four days and this is going to be a very good experience for her and I think I am going to see her in the near future. It is in Thailand and she is a Thai girl, I feel really bad for her for the last hole."
Ariya only secured her Ladies European Tour card in December when, as the world number two amateur, she romped to a five-shot victory in the qualifying school tournament in Morocco.