The Northern Irishman carded eight birdies and one bogey in a seven-under-par round of 64 at Royal Aberdeen to take a one-shot lead. It came just hours after Swede Kristoffer Broberg, one of the first players to start, had himself lowered the course record to 65.
“Everything was pretty much on,” said McIlroy, who drove the green at the par-four, 436-yard 13th hole. “I controlled my ball flight really well which is the key to me playing well in these conditions and on these courses.
“It would have been nice to make one or two more coming down the last few holes but I’m not going to complain about a 64, I played really well and obviously it’s a great start to the tournament.
“I like the course, it sets up well. It’s a nice mix of strategic play and then there’s times when you can be aggressive and take the driver out.”
Two-time Major winner McIlroy won the PGA Championship in May and will head to Hoylake as one of the favourites to win the Open.
American Phil Mickelson, who did the Scottish Open and Open Championship double last year, finished among a group on three under par, one behind England’s Luke Donald.