The four-time major winner, who turns 29 tomorrow, carded a three-under-par 68 at Quail Hollow to sit one off the clubhouse lead.
“I love this place,” said McIlroy of a venue where he has won on the PGA Tour – in 2010 and 2015. “I feel like I don’t have to play that good and I can still get it around. It’s a very comfortable golf course for me.”
Chasing a career grand slam, McIlroy began the final round at Augusta National three shots off the lead and closed to within a shot of eventual winner Patrick Reed after two holes, but faded to close with a 74.
In his first outing since then, the Northern Irishman started with a birdie and added four more in a pleasing opening effort that was helped by his TrackMan.
“It’s funny as I was hitting the ball left in the pro-am,” he revealed. “I thought it was because I was getting underneath it. I thought my swing plane and my path, I was getting inside out. But I wasn’t at all, it was actually the other way, it was more clubface.
“The clubface was coming in just a touch left at impact, and then with the speed that I have, it just accentuates it.”
McIlroy said it took only five swings to correct the problem, which was essentially feeling as if he is “holding” the clubface square longer through impact.
Englishman Tyrrell Hatton went one better than McIlroy with his opening effort in Charlotte after finishing birdie-birdie, to share the clubhouse lead with American Peter Malnati.
Paul Casey and Ross Fisher shot matching 69s but Phil Mickelson had to settle for a 72 despite sharing the lead with McIlroy on three-under early on.
Masters champion Patrick Reed was among the later starters along with Tiger Woods and US open champion Brooks Koepka.