The in-form McIlroy enters the weekend with a four-shot lead at Hoylake after carding consecutive six-under 66s.
American Dustin Johnson is outright second at eight under, two shots ahead of countrymen Ryan Moore and Rickie Fowler, Italian Francesco Molinari, Spain's Sergio Garcia and South Africans Charl Schwartzel and Louis Oosthuizen.
Johnson said he was happy with the position he was in and wants to stay focused on his own game.
"It's fine. I'm glad I'm in the last group. I'm going to go out and play my game," he said.
"I can't worry about what he [McIlroy] is doing. Just go out there and try to shoot a big number."
Molinari said: "It won't be easy trying to catch him up. We're here to try and we will do that over the weekend."
Garcia hopes tricky conditions see McIlroy drop back into the chasing pack.
"He's a wonderful player, we all know that and he's going to be difficult to beat but we'll see," he said.
"You know, when it plays tough like this, anything can happen out there."