A tight battle unfolded at Jack Nicklaus Golf Club Korea, with Larrazábal finding himself in a five-way share of the lead on nine under when he reached the turn following two front-nine birdies.
The Spaniard slipped from the summit after dropping his first shot of the round at the tenth but roared back, making four birdies in the next five holes to open up a three-shot lead.
He then safely parred his way home to complete a closing 67, finish the tournament on 12 under par and claim an eighth DP World Tour title just a couple of weeks before his 40th birthday.
Dane Marcus Helligkilde signed for a fourth-round 68 to finish in solo second on ten under, one clear of home favourite Park Sanghyun, Spain's Jorge Campillo, Dutchman Joost Luiten and Scotland's Scott Jamieson.
Larrazábal went into the final round one shot off the lead having bogeyed the 17th when he returned to complete his third round on Sunday morning.
But he took advantage of both of the front nine's par fives - the third and seventh - in round four to share the lead at the turn.
After starting the back nine with a disappointing bogey, Larrazábal bounced back with two consecutive birdies from around five feet at the 11th and 12th to grab the outright lead on ten under.
He created another good chance at the par-three 13th but was unable to convert his 15-foot putt.
A successful 20-foot birdie effort on the 14th green stretched Larrazábal's lead to two strokes before he got a lucky break at the 15th.
His tee-shot appeared to be going out of bounds but a fortuitous bounce sent the ball back down the slope and onto the cart path.
He made the most of his break, using his second shot to get the ball back in play before lifting his approach to two feet to set up a bonus birdie.
Holding a three-shot lead with three holes remaining, Larrazábal safely parred the 16th and 17th before finishing his round with another par on the last to clinch the trophy.
He said: "It’s amazing. In two weeks I’m turning 40. I’m not a long-hitter. To play against all these 20-year-old guys now that hit the ball 40 yards over me, and to beat them is unbelievable.
"To do it here in Korea, where we have not come for ten years and where I love to play. Now it’s one of my favourite places in the world.
"I will be back to Korea to defend this title and hopefully many more times.
"My older brother is getting married on Saturday.
"I don’t know if I’ll bring the trophy to the wedding but I’m sure we’ll celebrate 95% his wedding, and a couple – not too many – of drinks celebrating my title.
"It’s my birthday the week after and then flying to the U.S. PGA Championship in Rochester, New York.
"Seven out of nine weeks on mainland Europe finishing at The Open, and then holiday time."
by DP World Tour