Both players were 9-under 279 after 72 holes.
Castrale shot 1-under 71 in the final round, while Ochoa -- the No. 1 ranked women's player in the world -- ballooned to a 2-over 74, and dropped to 0-4 in her career when competing in sudden-death playoffs.
It was Castrale's first tour victory.
"I don't know if it's quite hit me yet," said Castrale, who won $390,000. "I stayed patient and it worked out. It was fun out there."