The Northern Irishman, the pre-tournament favourite, received loud support from the packed galleries at Royal Liverpool, scene of his Open triumph in 2014 after which he won the US PGA title and looked set for domination.
But he endured a frustrating day with his driver a little off and putts refusing to drop and at the 18th he faced a crisis when he left a bunker escape in the sand before playing a remarkable second attempt from a horrible stance.
That piece of magic enabled him to escape with a par five and post an even par 71 to sit five shots off the lead - a gap he will hope to reduce on Friday.
"I wouldn't have been too happy walking off the 18th with a bogey, especially after the two shots I hit in there," McIlroy, who missed a sitter to bogey the eighth and was two-over after 12 holes as the wind picked up, told reporters.
"When you hit it into these bunkers you're sort of riding your luck at that point. You're just hoping to make par somehow and get out of there. Overall, to get it back to even for the day, I'm pretty pleased with that."
McIlroy came close to winning last year's Open when he led into the final day only to be reeled in by Cameron Smith (29).
He was second at the US Open in June but his win at the Scottish Open underlined his favourites' tag.
So there was concern when his game failed to fire on Thursday before back-to-back birdies at 14 and 15 had the crowd roaring its approval.
"A few putts started to go in on the back nine for me," he said. "Hopefully I've got my eye in and I can build on that over the next three days. Two over through 12, I think walking to the 13th tee I probably would have taken even par to finish the day.
"That's exactly where I ended up. It wasn't the easiest of days. But I'm still right in there.
"Just go out there in the morning, shoot something in the 60s, and I'll hopefully be right in the mix."
