The 23-year-old from Thailand shot a 3-under 68 for a 12-under 272 total Sunday at Wilshire Country Club in the tour's return to Los Angeles after a 13-year absence.
Seven-time winner Ariya tied for 24th after a 70. She joined the predominantly Asian crowd to follow her older sister's final holes, crying as Moriya two-putted to close out the win.
Hall of Famer Inbee Park shot a 68 to tie for second with Jin Young Ko (70).
So Yeon Ryu (68) finished fourth at 7 under. Caldwell County native Emma Talley (67) and Eun-Hee Ji (71) tied for fifth at 6 under. Talley's fifth place finish is her best ever on the LPGA Tour.
