Ariya who just won the Canadian Open last week was trailing Masson a one stroke going into the final hole. But a poor tee-off cost her a drop shot before she ended with a bogey.
Her total score of 14-under-par 274 placed her at joint fifth along with world No 1 Lydia Ko of New Zealand and Suzann Petterson of Norway.
Masson shot a 67 and a total 16-under-par 272 for her maiden win on the LPGA Tour. A stroke behind at tied second were Karine Icher of France, Minjee Lee of Australia and Mi Hyang Lee of South Korea.