McIlroy, who finished his round with a 10-foot birdie on the 18th, holds a two-shot advantage over Americans Justin Thomas and Bubba Watson at Club de Golf Chapultepec, close to Mexico City.

After Adam Scott's triumph in the Genesis Open last week, the Australian contingent has made a disappointing start to a tournament that saw only 18 players from the 72-man field break par.

Zach Murray is best placed of the Aussies, levelling par with a score of 71, one shot ahead of Scott Hend and two ahead of Cameron Smith.

Scott and Marc Leishman are tied a shot further back in 49th place, with Dubai Classic winner Lucas Herbert carding a four-over 75.

This is the only World Golf Championships event that McIlroy, who made an eagle and five birdies, has not won as he bids to join Dustin Johnson as the only players to triumph in all four tournaments in the series.

"I like this place, like the golf course, and have always played well at altitude for whatever reason that is," he said.