The 19-year-old Northern Irishman had missed cuts during the last three weeks.
You get days when you read the lines perfectly and you know every putt is going in, McIlroy said.
Garry Houston (66) chipped in for a birdie on the 18th hole for a share of second place with Kyron Sullivan and Julio Zapata. A large group at 67 included defending champion Brett Rumford, who birdied the first three holes.
Miguel Angel Jimenez, a member of the European Ryder Cup team, bogeyed the last three holes for a 68.
McIlroy needed only 26 putts. His only bogey came at the 12th where he drove into a bunker. His lowest round was a 61 in the Northern Ireland amateur event at Royal Portrush.
Ive only been missing cuts by one or two shots, he said. I just feel like Ive been making silly mistakes. I feel once I have a little bit of form, I wont make them.
Former U.S. Open champion Michael Campbell shot 69.