The Northern Irishman currently holds the clubhouse lead after producing six birdies in a bogey-free round to finish one shot ahead of Matteo Mannassero.
When asked by BBC Sport if it was the perfect round, McIlroy said: "It sort of [was], especially in the first round of an Open. I couldn't ask for anymore. I stuck to my gameplan, focused on the par fives and tried to pick up other shots. For the most part my ball was under control and I'm very happy."
Meanwhile, Tiger Woods, who has recently returned from injury, is three shots off the pace after hitting two consecutive bogeys, but remains in contention with a first-round 69.