McIlroy, returning to the site of his first European Tour win in 2009, had seven birdies and an eagle for a 63 and two-stroke lead over Edoardo Molinari. Molinari had an eagle at the par-4, 351-yard second hole and posted one bogey on the day, that coming at the par-5 18th.
Gallacher, the tournament defending champion, played in the same group as McIlroy and world No. 1-ranked Tiger Woods. Woods had a bogey-free, 4-under 68. He had nine consecutive pars to complete his round.
McIlroy played the second nine of the Emirates Golf Club first Thursday and opened with two pars. He then posted three straight birdies and added birdies at 16 and 18 in making the turn at 5-under.
He had a birdie at the second hole and eagled the par-5, 568-yard third hole with a 10-foot putt. He got to 9-under with a birdie at the par-3 seventh.