The former No. 1 ranked player fired a second straight 6-under 66 to grab the halfway lead. After a bogey on the first hole, McIlroy bunched seven birdies into his round giving him 13 in the first two days of the tournament.
Prior to Friday's play, McIlroy has put up a cumulative score of 15 over par in second-round action this year, compared with 55 under for the opening round, and 39 under on the weekend.
He holds a 4-shot lead over Dustin Johnson whose 65 was the low round of the day.
Among those that trail by six shots are Sergio Garcia and Rickie Fowler.
Defending champion Phil Mickelson shot a 2-under 70 to leave him at even par.
Tiger Woods struggled to a 5-over 77 including a final-hole birdie that allowed him to just make the cut.