Sixteen-year-old American Lexi under 67 Saturday to win the Dubai Ladies Masters by four strokes.
Thompson finished at 15-under-par 273 for her second professional title. She was the second-youngest winner in Ladies European Tour history behind Amy Yang. Yang, who won as an amateur in 2006, was four months younger than Thompson at the time of her victory.
The young American carded back-to-back birdies from the second before dropping a shot on the par-three seventh. Thompson, who fell behind Lee-Ann Pace with that bogey, atoned for that mistake with a birdie on No. 9, and she made it two in a row with another birdie on the 10th.
Thompson posted two straight birdies for the third time in her round, at 13 and 14. She faltered to a bogey on No. 17, but closed the tournament in style with her fourth birdie in four days at the par-five 18th.
"It feels amazing. I feel really honored that they invited me back," said Thompson, who tied for 22nd last year. "I've been working on my game really hard and it's paid off. I'm going to continue working hard and just trying to improve every tournament."
Pace had two birdies and an eagle in the first six holes to jump to 12-under. She played the last 12 holes in one-over par for a three-under 69. She ended alone in second at minus-11.
Sophie Gustafson managed a one-under 71 to take third at 10-under-par 278. Becky Morgan (70), Stacy Lee Bregman (70) and Pernilla Lindberg (71) shared fourth place at nine-under-par 279.
Michelle Wie (72) tied for 12th at minus-five.