World number two McIlroy made three birdies, including a 13ft putt on the par-five eighth, in blustery conditions.
The four-time major champion has been working with Tiger Woods’ former coach Butch Harmon to make minor adjustments to his game.
“He gave me a tiny little something that I went with. It’s felt a little better over the last two weeks and felt pretty good out there,” McIlroy told PGA Tour.com., external
“What I’ve been trying to do the last couple weeks is no different than what I’ve been trying to do previously. He just sort of gave me a different way to do it.”
Scotland’s Martin Laird and Englishmen Tommy Fleetwood and Matt Fitzpatrick are eight shots off the lead on one under.