McIlroy made four birdies and no bogeys in the third round on the Blue Monster, his 4-under 68 getting him to 12 under for the week and three shots ahead of Adam Scott and defending champion Dustin Johnson with 18 holes left in the first World Golf Championships event of the season.
Australian snaps win drought with Honda Classic victory
Scott said, "I was trying to get a ball dry there and eventually did on my fifth."
McIlroy bested Tiger Woods to win the title in 2012 - rising to number one in the world for the first time.
American golfer moves back to number four in the world
Spieth misses the cut; Johnson, Watson and McIlroy keep pace
Paul Maycock took home the honours in the Division B category.
Struggling Jordan Spieth cards 79 at Northern Trust Open
Masters and US Open champion Spieth, playing this week in his fourth Northern Trust Open, has made no secret of how highly he would value a first victory at Riviera.
The leading 12 players shared a prize fund of $13,000 with Gallegos walking away with a winner's cheque for $3,000.
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