Thompson, who started the final round with a four-stroke advantage, carded a four-under-par 68 for a 20-under total to register a seventh LPGA Tour win of her career and third title since July.
If the 21-year-old was hoping for an afternoon stroll in Pattaya she was in for a shock when playing partner Chun In-gee mounted an early assault with birdies on the first three holes that cut Thompson's lead to one shot.
The South Korean bogeyed the fourth, however, to double the American's advantage at the top and Chun was unable to get any closer once Thompson had moved further clear with an eagle on the par-five 10th.
“She played great the whole day and that birdie rampage from the first when she got three in a row was amazing,” Thompson told reporters after a win that ensures she will leapfrog compatriot Stacy Lewis to become the top-ranked American woman.
“But I was just trying to play my own game, make birdies and play a solid round. My goal going into the day was to get to 20-under and make a lot of birdies.”
Thomspon, who claimed her only major victory to date at the 2014 Kraft Nabisco Championship, will move behind Lydia Ko and Park In-bee in Monday's rankings and feels honoured to find herself among such elevated company.
“It means the world to me,” Thompson added. “I may be out here representing myself but I am also representing my country.
“It's a huge year with the Olympics but I am just focused on my own game, not anyone else's and its an honour and a privilege just to be out here following my dreams.”
Chun overcame a double-bogey six on the 17th hole to birdie the last and claim second place on 14-under, one shot clear of American Jessica Korda, who shot a best-of-the-day eight-under 64, and defending champion Amy Yang in a tie for third.
Original source: Lexi rises to No 3 in rankings