He also wasn't thinking about last year, when he walked off the Champion Course at PGA National Resort & Spa midway through his second round.
He was focused on playing the 18 holes ahead of him and he played them better than anyone, putting together a bogey-free, seven-under-par 63.
"It's a new tournament," McIlroy said. "You can't really let any other thoughts creep into your mind, because it is such a tough golf course."
A Northern Ireland native who has a home in Palm Beach Gardens, McIlroy has a one-shot lead over Russell Henley.
Rory Sabbatini, the 2011 champion, shot 65 along with William McGirt and Jamie Donaldson. Five others were tied for sixth at 66 on a day when the wind hardly blew and rain threatened but never fell.
When McIlroy won here, he moved up to No. 1 in the world rankings. His withdrawal here last year started his slide to his current No. 8 ranking.
He's feeling much better about his swing, as well as his golf balls and clubs, which were new to him last year after he signed a big contract with Nike.
"Golf's a very fickle game, because when you're on and you're playing the way I'm playing right now and feeling very comfortable with everything, you wonder how it ever felt so uncomfortable," McIlroy said. "And then when it feels so uncomfortable, you wonder how it ever felt so comfortable. And it's just a tiny thing that needs to click."
McIlroy, 24, was clicking Thursday. He hit 10 of 14 fairways and 14 greens, got up and down all four times and needed only 25 putts.
His first par save was on the first hole, then he birdied Nos. 2 and 3. A "great" par save on No. 9 was followed by three consecutive birdies.
"That really kept my momentum going on the back nine," said McIlroy, who drove into the right rough, came out 40 yards short of the pin, chipped to 11 feet and made the putt. "So if you don't make that par save, maybe things would be different."
He made a 12-foot birdie putt on the par-three 17th, then took the lead with a birdie on the par-five 18th after he hit his second shot into a greenside bunker and blasted out to four feet.
"You know, coming in this week, I knew that I was playing well and I just wanted to try and get off to a good start," McIlroy said. "It was nice to do it, regardless of what happened last year."
Henley won his very first PGA Tour event as a professional, the 2013 Sony Open in Hawaii, and had two other top-10 finishes last year. This season he has missed the cut in four of nine events, his best finish a 27th.
He said he had gotten too technical with his swing, so he tried a different approach in his last round, a 66 at Riviera that came after an opening 78.
"I just said, ' … I'm going to play golf today and I'm going to swing hard and I'm going to chase it.' I told myself I'm going to do that from now on," he said.
Starting on the back nine, Henley birdied five of his first six holes and added one birdie on his second nine. He hit 17 greens and had 29 putts.
"I got off to a great start by hitting fairways and hitting greens [and] giving myself some chances," Henley said.