The Spaniard, who was runner-up at Doha Golf Club last year, shot a seven-under-par round of 65 to surge to the top of the 72-hole leaderboard, where he was joined by Ilonen (66) on 18-under-par.
On the first playoff hole, the pair drove within a few feet of each other on the par-five 18th before Garcia sent an arcing 7-iron to within 12 feet of the hole but couldn't convert his eagle putt after Ilonen had also pushed his wide of the cup.
Back down the 18th they went and again they would halve the hole in birdies. Like before, Ilonen missed an eagle putt while Garcia splashed a hefty bunker shot to within a couple of inches.
On the third attempt, Ilonen pushed his drive out to the right before finding the same bunker as Garcia on the hole before. He couldn't get it close enough for a tap-in and missed his birdie putt, leaving Garcia with a tiddler for the title which he couldn't miss.