The Co. Down man finished with an opening round 77 to leave him 11 strokes of the pace
Rory McIlroy insists the most important thing for him now is to "stay positive" after carding a seven-over-par opening round at the US Open.
McIlroy finished his delayed round with three consecutive bogeys and will have to work hard if he is to make the cut, which is projected at four over par.
"I don’t need to swing perfect but I just need to be able to play one shot and know that I know where it’s going to start and know where it’s going to finish," he told reporters.
"I know what I’m doing, but it’s hard to change it out there. It’s been hard to give it any sort of time this week to work on it. Whenever I got off the course last night, I knew – and it was just hard to work on anything.
"With the way the golf course is, with it being so soft, I might just go out there in the second round and hit a lot of drivers and try to be as aggressive as I possibly can be."
"For me the toughest thing is just trying to stay positive and not get too down on myself. Get out there tomorrow morning and try to play well and make it into the weekend.
"Right now I’m just trying to stay as positive as I can."