The Northern Irishman believed he'd done everything he could to prepare for the tournament being held on his home soil for the first time since 1951. But there was one moment McIlroy admitted he could never have prepared for.
"The way they do it at The Open almost feels like a ring walk for a boxer. People are cheering. You come down the steps and through a tunnel and onto the tee box, and there's this massive ovation," McIlroy recalled.
"And I'm like, 'Woah!' That was the first time I felt it - 'Jesus, this is huge!' And I hadn't prepared myself for it," he continued. "I had prepared for the golf, and the golf course, but I hadn't prepared for that feeling. And I don't know if I could have prepared for that feeling."
McIlroy, who added he's always nervous before heading to the first tee, infamously hooked his opening tee shot out of bounds, which led to a quadruple-bogey eight.
"I was overwhelmed by the support," he said. "I looked up and just thought, 'Holy shit!' So that was the moment, and then nervous, real nervous."
The nerves were even more apparent when McIlroy asked his caddie, Harry Diamond, what club to hit on No. 1.
"I said to Harry before the first tee shot, '4-iron?' I had played the 2-iron the week before in Scotland and wasn't fully comfortable with it, but 4-iron wasn't the right club," McIlroy explained. "He said, '2-iron is not reaching the bunker. Hit the 2-iron.' And I said, 'OK.'"
McIlroy shot a 79 in Round 1 and narrowly missed the cut by one shot after shooting a 65 on Day 2.
In the end, McIlroy can apply a phrase he commonly uses to his disappointing performance at the 2019 Open Championship: win or learn.