"I'm very confident with my driver at the moment".
Johnson, 33, has enjoyed plenty of success at WGC events and first won this tournament in 2015, when it was held at Trump National Doral in Miami.
Louis Oosthuizen ended the day on top of the leaderboard.
The long-hitting American already has three top-10 finishes in four PGA Tour starts this season, including a January victory at Kapalua, and will tee off at Club de Golf Chapultepec with an eye on gaining some momentum ahead of the April 5-8 Masters. "The first 15 holes tee to green, I was really solid, hit a lot of fairways, a lot of greens".
India's Shubhankar Sharma, a two-time victor on the European Tour this season who is out to improve from his current 75th in the world to a top 50 spot that would see him into the Masters, was five-under through 16 when play was halted by lightning, with world number two Jon Rahm alone in the clubhouse on four-under 67.
That secured his World Golf Championship debut in Mexico City via the top 10 on the European Tour's Race to Dubai and the 31-year-old from Hexham made the most of his opportunity in an elite 64-man field competing for a winner's cheque of $1.2million from a prize fund of $7.2million.
India's Shubhankar Sharma, England's Chris Paisley and American Xander Schauffele who all lurk menacingly just one stroke behind the leader.
"I didn't want to come here and just be happy to be part of it and just make up the numbers", he said. But I did putt pretty well. "To play as well as I did and shoot a great score against the world's best players and to be right up there, I'm just delighted".
Last year's runner-up, Briton Tommy Fleetwood, is coming off a fourth-place finish at the Honda Classic and will be eager to return and seek his first PGA Tour win. "You're always very happy when you start with such a low round, especially for me. I felt like I was just struggling all day, just grinding", said Johnson, who finished with a 2-under 69 and is tied for 13.
He played with Johnson and Jon Rahm, who also had enough mistakes to limit him to a 67. The South African carded a blemish free 64 which included five birdies and an eagle on the par five 15th hole.