The Northern Irishman slumped to two over par after 13 holes, though quickly rattled off three birdies to finish one under at the Woo Jeong Hills Country Club.
But McIlroy admitted his slow start was due to being a “little rusty” having not played since last month’s BMW Championship in Illinois.
“I just wasn’t very comfortable with the tee shot,” he said.
“I took a long time to get settled over it and then just didn’t make a very good swing.
“Some of the pin positions were brutal and very hard to get them close. And when you did you left yourself tricky putts.”