A switch of footwear and extra padding helped the world number two from Northern Ireland as he sought to complete his preparations for the second major of the year.
“I figured it out and separated the little toe from the other ones and a bit of cushion around it definitely helped,” he said. “And then just going to a bigger shoe and a different style of shoe as well, a little wider and a little softer in the toe box.
“It’s half a size up and it’s a wide fit so there’s just a bit more room.”
McIlroy says he does not feel pain while hitting shots but the 7,394 yard Aronimink is a demanding and undulating walk. “I was pleasantly surprised how good it felt,” he said.
“Walking downhill, whenever your foot slides into the very end of your shoe is when it maybe gives me a bit of bother but it’s totally fine. A mountain out of a molehill.”
McIlroy, who successfully defended his Masters title at Augusta last month begins his attempt to win a third US PGA title at 13:40 BST (08:40 local time) in a group that includes fellow major winners Jordan Spieth and Jon Rahm.