He began with a 2-over-par 74 on the golf tournament's first day, but his scores in the next two rounds were 66 and 68, respectively.
He closed with a 5-under 67 in the final round, which included birdies at four of the last six holes.
His final score was 13-under 275, one-shot better than native Carl Schwartzel, who led the event after the second and third rounds.
"I have not been hitting the ball very straight off the tee and Saturday was terrible, I was pulling everything," said Quiros, who is a first-time winner. "I can't imagine I won (but) I am very happy."
Schwartzel lost his chance to win the event by ballooning to an even-par 72 on Sunday.
England's Lee Westwood (73) was third at 9-under 279.