Taking up where he left off when finishing his second circuit at Sheshan International Golf Club in Shanghai, McIlroy carded five birdies in a bogey-free effort as he moved to 15-under-par in the $10.25 event.
The world No 2, who is bidding to land his first European Tour title since 2016, leads by a shot from South African Louis Oosthuizen (65), with defending champion Zander Schauffele (68) one further back along with halfway leader Matthew Fitzpatrick (70).
“I probably played the best today that I’ve played all week,” said McIlroy as he reflected on a round that saw him make birdies at the second, sixth, ninth, 14th and 18th holes. “I drove the ball well. Hitting my irons pretty good for the most part.
“I feel like I didn’t quite get as much out of the round as I could have, but I’m not going to complain. I’m in the lead going into tomorrow, so just need to rest up and try to get out there and play another good, solid round of golf.”
McIlroy, who won his first WGC title in the Bridgestone Invitational in 2014 before adding the Cadillac Match Play the following year, is aiming to record his fourth success this year after wins in the Players Championship, RBC Canadian Open and Tour Championship on the PGA Tour.
“I keep saying, I think my consistency this year, I’ve been able to take that to another level to what I’ve been able to do previously,” he added. “Right now, the game feels pretty simple. I know that it’s not going to feel like that all the time, but when it does, you have to take advantage of that feeling.
“I’ve given myself another opportunity to win a very big golf tournament, a tournament that I’ve never won before. I want to go out there and be committed, play aggressively, and shoot a good number.
“I took a lot from the win in Canada earlier this year. I went out tied for the lead, and I just said from the start, I’m going to keep my foot down and I’m going to go for everything. It was a good lesson that when you do have something right there, in front of you, a tournament to win or something to achieve, you just have to grab it with both hands, and that’s what I’ll do tomorrow.”
Oosthuizen, the 2010 Open champion, burst out of the blocks with five straight birdies before adding four more on the back nine as he set up a chance to claim his first WGC title.
“It was a very fast start,” he said. “Today I really struck the ball really good with my irons. The driver, I had a few awkward swings out there, but at the end I started hitting it good. I played with Rory the last two rounds last week. He’s absolutely striping it. I need to play really good golf tomorrow.”
After opening with rounds of 70 and 69 to sit joint-11th at the halfway stage on his WGC debut, MacIntyre slipped to a share of 22nd following a 73 that was a mixed bag of four birdies and five bogeys in the company of Justin Rose and Tony Finau.
The 23-year-old Scot was out in two-over after dropping shots at the sixth and ninth before mixing three birdies with three bogeys on an up-and-down back nine on a day when his driving was not quite as good as it had been in the opening two circuits.
On the PGA Tour, Russell Knox heads into the final two rounds of the Bermuda Championship just two shots off the lead in joint-fourth after opening efforts of 64 and 69 to sit on nine-under-par.