The Spaniard's 12-under 276 at the Jack Nicklaus Golf Club Korea was good enough to secure his eighth European tour title after starting the final round one shot back.
Larrazábal closed to a five-way share of the lead at the turn at 9-under and pulled away with four birdies in the next five holes to open a three-shot lead that he never relinquished.
"I love to compete. I love to fly out here, to see all these young guys hitting it miles and try to beat them," Larrazábal said. "And that's what makes me the happiest guy in the world."
Denmark's Helligkilde finished his fourth round with a 68 to take second place, holding off a four-strong chasing pack that included home favorite Park Sang-hyun.