The 19-year-old native of Northern Ireland has a three-round total of 13-under 200, with Argentina's Juan Abbate (69), Alejandro Canizares (69) of Spain, Frenchmen Christian Cevaer (65), Jean-Francois Lucquin (69) and Julien Clement (67), Scotland's Robert Dinwiddie (64) all knotted in second place at 9-under 204.
"It was definitely more satisfying than the 63 (he shot Thursday) given the circumstances," McIlroy told reporters.
"Five-under was a very good effort. This is my first time in this situation and I'm just really looking forward to tomorrow. I don't want to take my foot off the pedal," he said. "I've a four-shot lead and I'd like a six-shot lead tomorrow. Trying to make birdies is the way I play my best (and) it would be fantastic to win."
Clement does not have a European Tour card and is ranked 779th in the world.
Swim Week Miami Beach 2014 [PHOTOS]