SEOUL, October 17, 2013 (AFP) - The two-time major winner is the star attraction at the Woo Jeong Hills Country Club where the $1 million One Asia Tour event is the Northern Irishman's first taste of competitive golf after a month-long break.
McIlroy, who lies in lowly 60th position on the European Tour standings, was two-over par with five holes to play before bouncing back with three birdies to complete a first-round score of one-under.
The 24-year-old world number six exchanged a bogey with a birdie on the front nine before coming away with a double bogey on the par-3 13th after finding water off the tee.
After his round, McIlroy admitted he felt "a little rusty" after four weeks off and had to battle to finish under par for the day.
"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."
He added: "It was tough, some of the pin positions out there today were brutal, just cut on slopes and very hard to get close to them. And when you did get close to them, you left yourself very tricky putts."
The 2011 US Open champion and 2012 PGA winner is in a seven-way tie, three shots off the leader -- South Korean veteran Jang Ik-Jae.
Jang fired the only bogey-free round of the day to shoot a 67 and holds a one-stroke lead going into Friday's second round.
It included a spectacular eagle on the par-4 10th, when he found the bottom of the cup with a 9-iron from 155 metres (170 yards) away.
Jang led the 2005 Korea Open through three rounds but shot a 76 on the final day to drop to a tie for 14th.
A two-time winner on the Japan Golf Tour, Jang is seeking his first victory on native soil since 2005.
"I didn't hit it too well off the tee," Jang said. "But I hit some good recovery shots and putted well."
In second place on three-under par was the South Korean trio of Kang Sung-Hoon, Yoon Jung-Ho, Han Min-Kyu and Eric Mina of the United States -- the highest-placed non-Korean.
Defending champion Kim Dae-Sub of South Korea was one shot further back on 69.
Starting his day on the back nine, Kim three-putted for a double bogey on the par-4 11th, but picked up four birdies later.
Tricky pin placements on the 6,591-metre (7,208-yard) layout meant only 18 players broke par on the first day.
McIlroy was making his third appearance at the Korea Open. He tied for third in 2009 and finished runner-up to Rickie Fowler in 2011.
McIlroy, whose struggles this year have been well documented, cannot afford another disappointing week if he is to qualify for the season-ending Dubai World Tour Championship, where he is defending champion.
His weeks-long break from golf came after he failed to qualify for the USPGA Tour Championship and coincided with an acrimonious split from his management company.
Earlier this week he refused to comment on rumours in the British media that his high-profile relationship with the Danish tennis star Caroline Wozniacki was over.